Ruff pretty much follows the same rules as black, and can be made identical with some options tweaking.

So when I moved several projects from black to ruff, there were no changes made to the code.

That wasn't my experience. I tried it on a large project and about 1% of lines were changed. Not a big deal IMO but enough for naysayers to complain.

I find this hard to believe since black doesn't even have the same rules as black's next version and I never changed version without something being reformatted.

Also because of fun, if you reformat again with the older version it won't go back to as it was before :)