Using the command below, you can turn a mob into a balloon without using any mod or data pack.
To turn a mob into a balloon, you must obtain a Balloon Potion. You have to throw a water bottle and a phantom membrane to the ground to make a Balloon Potion or right-click on the sign on the side of the command box that is written: "[​GIVE POTION]".

When you have 5 or more balloons, you will gain a slow falling effect.
When you have 10 or more, you will start levitating

Watch on Youtube: https://youtu.be/YSMPCpW_lQk
Official command: https://torchcraftyt.github.io/Commands/Mob_balloon.html

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Triple-click to select all the commands then right-click and choose copy. Next, get in your world, and give yourself a command block (using /give @s command_block). Paste the command in the command block (using Ctrl+C or Cmd+C). Finally, place a Redstone block next to the command block.

Command: (triple-click to select all)
summon minecraft:falling_block ~ ~1 ~ {BlockState:{Name:"redstone_block"},Time:1,Passengers:[{id:villager,Health:0,Passengers:[{id:falling_block,Time:1,BlockState:{Name:"activator_rail"},Passengers:[{id:command_block_minecart, Command: 'gamerule commandBlockOutput false'},{id:command_block_minecart, Command: '/fill ~1 ~-2 ~0 ~5 ~2 ~4 minecraft:light_blue_concrete'},{id:command_block_minecart, Command: '/fill ~1 ~-1 ~0 ~5 ~1 ~4 minecraft:light_blue_stained_glass'},{id:command_block_minecart, Command: '/setblock ~0 ~1 ~2 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"black",GlowingText:0b,Text1:\'{"text":"Balloon"}\',Text2:\'{"text":"--"}\',Text3:\'{"text":"Made by"}\',Text4:\'{"text":"TorchCraft"}\'}'},{id:command_block_minecart, Command: '/setblock ~0 ~0 ~2 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"black",GlowingText:0b,Text1:\'{"color":"dark_blue","clickEvent":{"action":"run_command","value":"give @s lingering_potion{CustomPotionColor:917378,display:{Name:\\\'[{\\\\"text\\\\":\\\\"Balloon Potion\\\\",\\\\"italic\\\\":false}]\\\'},CustomPotionEffects:[{Id:27,Duration:999999,Amplifier:31,ShowParticles:0b,ShowIcon:0b},{Id:26,Duration:999999,Amplifier:41,ShowParticles:0b,ShowIcon:0b}]}"},"text":"[GIVE POTION]"}\',Text2:\'{"text":""}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'},{id:command_block_minecart, Command: '/setblock ~0 ~-1 ~2 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"black",GlowingText:0b,Text1:\'{"color":"dark_red","clickEvent":{"action":"run_command","value":"fill ~ ~-1 ~-2 ~5 ~3 ~2 air"},"text":"[UNINSTAL]"}\',Text2:\'{"text":""}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'},{id:command_block_minecart, Command: '/setblock ~2 ~1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=balloon-potion] at @s run particle minecraft:happy_villager ~ ~.3 ~ 0.1 0.1 0.1 1 10 normal",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:\'/execute as @e[tag=balloon-potion] at @s run kill @e[type=item,limit=1,distance=..1,nbt={Item:{id:"minecraft:phantom_membrane"}}]\',auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute as @e[tag=balloon-potion] at @s run tag @s remove balloon-potion",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~1 ~2 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"execute as @a store result score @s Balloon-UUID.0 run data get entity @s UUID[0]",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~1 ~2 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute as @e[tag=balloon-active] store result score @s Balloon-UUID.0 run data get entity @s Leash.UUID[0]",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~1 ~2 minecraft:chain_command_block[conditional=false,facing=south]{Command:"scoreboard players reset @a BalloonCount",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~1 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @a[scores={BalloonCount=10..}] run effect give @s minecraft:levitation 1 0 true",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~1 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @a[scores={BalloonCount=5..}] run effect give @s minecraft:slow_falling 1 0 true",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~1 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute at @e[tag=balloon-active] as @a if score @s Balloon-UUID.0 = @e[limit=1,distance=0] Balloon-UUID.0 run scoreboard players add @s BalloonCount 1",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~0 ~1 minecraft:chain_command_block[conditional=false,facing=up]{Command:\'execute as @e[tag=balloon-potion] run data modify entity @s Item set value {id:"minecraft:lingering_potion",Count:1b, tag:{CustomPotionColor:917378,display:{Name:\\\'[{"text":"Balloon Potion","italic":false}]\\\'},CustomPotionEffects:[{Id:27,Duration:999999,Amplifier:31,ShowParticles:0b,ShowIcon:0b},{Id:26,Duration:999999,Amplifier:41,ShowParticles:0b,ShowIcon:0b}]}}\',auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~0 ~1 minecraft:repeating_command_block[conditional=false,facing=west]{Command:\'/execute as @e[type=item,nbt={Item:{id:"minecraft:potion",tag:{Potion:"minecraft:water"}}}] at @s if entity @e[type=item,distance=..1,nbt={Item:{id:"minecraft:phantom_membrane"}}] run tag @s add balloon-potion\',auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~0 ~1 minecraft:chain_command_block[conditional=false,facing=west]{Command:"execute as @a[tag=unballoon] run tag @s remove unballoon",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~0 ~2 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"/execute as @e[nbt={ActiveEffects:[{ShowIcon:0b,ShowParticles:0b,Id:26,Amplifier:41b},{ShowIcon:0b,ShowParticles:0b,Id:27,Amplifier:31b}]},type=minecraft:player] run tag @s add unballoon",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~0 ~2 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute as @a[tag=unballoon] run effect clear @s minecraft:unluck",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~0 ~2 minecraft:chain_command_block[conditional=false,facing=north]{Command:"execute as @a[tag=unballoon] run effect clear @s minecraft:luck",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~0 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=balloon-active,nbt={HurtTime:5s}] run kill @s",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~0 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute at @e[tag=balloon-active,nbt={HurtTime:5s}] run particle minecraft:explosion ~ ~ ~",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~0 ~3 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute at @e[tag=balloon-active,nbt={HurtTime:5s}] run playsound entity.generic.explode master @a ~ ~ ~ .2 1.8",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~-1 ~1 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"/execute as @e[nbt={ActiveEffects:[{ShowIcon:0b,ShowParticles:0b,Id:26,Amplifier:41b},{ShowIcon:0b,ShowParticles:0b,Id:27,Amplifier:31b}]},type=!minecraft:player] run tag @s add balloon",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute at @e[tag=balloon] as @e[sort=nearest,type=minecraft:area_effect_cloud,nbt={Effects:[{ShowIcon:0b,ShowParticles:0b,Id:26,Amplifier:41b},{ShowIcon:0b,ShowParticles:0b,Id:27,Amplifier:31b}]}] run data modify entity @e[limit=1,distance=0] Leash.UUID set from entity @s Owner",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=south]{Command:"execute at @e[tag=balloon] as @e[sort=nearest,type=minecraft:area_effect_cloud,nbt={Effects:[{ShowIcon:0b,ShowParticles:0b,Id:26,Amplifier:41b},{ShowIcon:0b,ShowParticles:0b,Id:27,Amplifier:31b}]}] run kill @s",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=south]{Command:"execute as @e[tag=balloon] run effect give @s minecraft:levitation 300 10 true",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"execute as @e[tag=balloon] run effect clear @s minecraft:unluck",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"execute as @e[tag=balloon] run effect clear @s minecraft:luck",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~2 ~-1 ~3 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute as @e[tag=balloon] run tag @s add balloon-active",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~3 ~-1 ~3 minecraft:chain_command_block[conditional=false,facing=east]{Command:"execute as @e[tag=balloon] run tag @s remove balloon",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/setblock ~4 ~-1 ~3 minecraft:chain_command_block[conditional=false,facing=up]{Command:"execute as @e[tag=balloon-active,nbt=!{ActiveEffects:[{Id:25}]}] run tag @s remove balloon-active",auto:1b,conditionMet:1b,powered:0b}'},{id:command_block_minecart, Command: '/scoreboard objectives add Balloon-UUID.0 dummy'},{id:command_block_minecart, Command: '/scoreboard objectives add BalloonCount dummy'},{id:command_block_minecart, Command: 'setblock ~ ~1 ~ command_block{Command:"fill ~ ~ ~ ~ ~-3 ~ air",auto:1}'},{id:command_block_minecart, Command: 'kill @e[type=command_block_minecart,distance=..1,tag=!debug]'},]}]}]}