I'm pretty sure Android 11 has no restriction in copy&paste, that is one of the most fundamental functions after all. Maybe it is a bug in Pixel. I assume you were using the Files app to do copy&paste? I suggest you try a different file explorer (I never used any google device before but I assume it allows you to use different file explorers than Files?)
And you can always choose to connect your phone to a pc and copy&paste files easily as you do on a pc.
