NotchMindmacOS protects some folders even from apps you run: Mail, Messages, Safari history, Time Machine settings and other apps’ private data. Full Disk Access lets an app read them.
Who needs it
Backup tools, antivirus scanners, disk cleaners, and apps that read Mail or Messages to show notifications.
Grant it
System Settings → Privacy & Security → Full Disk Access, then turn the app on, or click + to add it. Quit and reopen the app afterwards.
Remove it
Turn it off in the same list.
Be choosy
It’s a broad permission. Give it to apps that clearly need it and say why. NotchMind, which I make, asks for it only for Messages and Mail notifications, the Inbox page and Focus names, and processes those on your Mac. If you don’t use those, you don’t need to grant it. See why NotchMind asks for Full Disk Access.