Big Sur on Macbook Pro M1 does not allow to add an Administrator account to a file
I actually had the same problem for some of my downloaded apps outside of the appstore .
Try this :

Press command + space and type terminal and press enter to open terminal

Paste this code in terminal and press enter .


sudo chmod -R 755 /path/to/app
Note : to get the path to app simply drag the file you can't open because of permission issues to terminal .
sudo xattr -dr com.apple.quarantine /path/to/app

Next paste this code with the path of the app and press enter .

You can open the file now with no permission problems .