Mail Settings
In the mail app, the light grey collum on the left that shows your mailboxes have disappeared. How can I get this back ?
MacBook Air 13″, macOS 11.6
I've read that using Force Quit, then re-open Mail often times brings them back into the sidebar.
Click Apple Logo upper left corner. Select Force Quit.
If that doesn't work, try entering safemode which runs system diagnostics and repairs things it finds wrong.
Start up your Mac in safe mode - Apple Support
