I'm afraid I don't really have the resources to check Apple’s betas for compatibility.
As far as Catalina is concerned, Keyboard Maestro was compatible with it at release for the most part, you just have to work around Apple’s bugs and figure your way through Apple’s security facilities.
I expect Big Sur will be the same, but only time will tell.
But, that said, I do have Keyboard Maestro building as a universal binary for arm and will hopefully get to test it on a Dev Kit next week, so that is at least promising.