The file can’t be found.

Hello paulfinn,

Thanks for using the Apple Support Communities. We understand that you're receiving an error message when attempting to open a file on your Mac running Big Sur.

What's the exact wording of the full error message?

If you perform a search for the file, are you able to locate multiple copies?

Can you tell us what type of file you're attempting to open?

Have you tried restarting your Mac and then attempting to open the file? Many times, a simply restart can correct minor issues you're experiencing with your device. Log out, sleep, wake, restart, or shut down your Mac

If you haven't done so yet, try booting up into safe mode and attempt to open the file. Then go ahead and restart your Mac to exit safe mode, and once you're up and running, attempt to open the file once more. How to use safe mode on your Mac

Keep us posted on how it goes.

Best regards.