No permission to scan with Brother printer & MacOS Big Sur 11.5.1

Find the Brother scanner app and try to run it directly in the Finder. It is probably inside a Brother folder inside /Library/Application Support. If running it directly once doesn't resolve the quarantine, try ctrl-clicking on it and choosing open.

What worked in my case after upgrade from Catalina to Big Sur (Brother MFC-9320cw) was to add my user admin permission to ~/Library/Image Capture/Devices/Brother Scanner.app, Get Info (Right Click or Command i or Finder-File Menu) and unlock at lower right corner then click the plus at lower left corner to add your admin log-in user & privilege.

Hope others find this helpful.

If I knew that installing OS Big Sur Ver. 11.5.2 would make my Brothers printer/scanner no longer work properly I would never have installed it. I do not see any improvement in the operation of my MAC with the new Big Sur OS. It just opened up a bag of worms. How did the Apple community come to the conclusion that Big Sur was an "improvement"?

Can I easily go back to my previous OS?

Or maybe try looking in /Library/Image Capture/Devices

if you see the Brother scanner app Control-click on it and then click Open.

Can I easily go back to my previous OS?

Yes, just erase your drive and restore from the backup you made before installing Big Sur.