The menu square pops up but with no text at all, and is blank every time I try to use the force touch trackpad to copy paste items.
Can't see any text in the little pop up window.
It sounds like some system resources aren't installed. I assume it was working before Big Sur. Would you consider running the Big Sur installer again? I hope someone else has some useful suggestions. Going to back to the installer seems like a big deal.
How about other accounts. Do you have any other user account you can check?
I'm running Big Sur with no problems. Most of what you read in these forums is from people with problems, and that can't be extrapolated to conclude that there are a lot of issues with Big Sur. Going back isn't easy. If I were you, I would just try to solve your problem. But it's your machine and your course of action is up to you. Also, macOS 11.1 is probably just a week or two away.