I got tired of trying to follow online circle generators and so I made this datapack. Generate a circle or sphere as large as your computer/render distance can handle. The guide is purely visual, allowing you to place blocks directly overtop of it, and I programmed my generator to closely (or exactly) resemble online generators.

Commands:

1. /trigger set_diameter.circular add|set <value>
2. /trigger set_orientation.circular set <value>
3. /trigger total_clear.circular
4. /scoreboard players set command_limit circular.main <value>

Use command 1) to generate the circle/sphere guide, centered on the player

Use command 2) to set the guide orientation
  0 -> Horizontal circle (xz plane)
  1 -> Vertical circle (xy plane)
  2 -> Vertical circle (yz plane)
  3+ -> Sphere

The guides do not self delete, so it is up to the player to use command 3) to delete unnecessary guides.

Command 4) limits the amount of commands circular can use per tick towards generating circle/sphere guides. By default this value is 32,000. Set the value higher for faster generation, set the value lower to reduce computational strain. I recommend staying above 6,500 and below 65,000.

In practice its best to create circles/spheres that will fit within your/your servers render distance. Max diameter = (Render distance in chunks) x 32, giving a maximum of 1024 blocks at 32 chunks render distance and 64 blocks at 2 chunks render distance.