I don't know if this is related to Big Sur or not – it wasn't a problem in the beta!
I used to be able to copy service items between presentations using the standard Cmd C and Cmd V (or the secondary click menu).
Today...

...doesn't put anything on the clipboard.
With this particular 'content' item I have a workaround that just involves copying the contents and resetting the background.
I would be good, however, if the Copy function could be restored.