I've had this odd "aliases could not be set" error issue for a while, which prevents me from being able to set before/after. Does anybody have a solve for this?

I gave it a go and it doesn't reproduce in my 20.0.625 mac install. I'd try the latest daily build and if that still reproduces, log a bug with your scene file and explain the exact steps to reproduce using it.

this is a delightful and long standing bug. welcome to the party, pal.

the workaround is to right-click the channel in the anim editor list, and you can get to the extrapolation from there

cheers,
chrisg