And basically a lot of reports on Reddit. Eg.:
https://old.reddit.com/r/ErgoMechKeyboards/comments/ubcxup/e... https://old.reddit.com/r/ErgoMechKeyboards/comments/umg2j5/e... https://old.reddit.com/r/ErgoMechKeyboards/comments/lj3n45/p...
Of course, these are just anecdotes and we don't have good research into all the individual designs, but there seems to be a pattern. The movement is also similar to what causes texter's thumb.
At any rate, I am not an ergonomics professional, so if you are switching to a more ergonomic keyboard because you have pains, you should ask and expert what works and what doesn't.