Hi there, welcome.
First of all, after booting from a snapshot you should always restore it from the BTRFS assistant, and then reboot. This is not mentioned, so I assume it was not done. Don’t do anything (e.g. install, update, etc.) before that.
I’m not sure this will bring you back to a functioning system now, but it should be done.
Just a few additional hints:
This was a mistake because there was a kernel update (and a lot of other suff), so a reboot was needed.
This should be always avoided. There are things that could be done to save your… E.g.