

System integrity protection is not a new feature of macOS 11 Big Sur, but has been active on the Apple Mac since OS X 10.11 El Capitan. Switch off SIS or SIP: Delete installer by deactivating system integrity protection

If you get stuck with this, try the instructions under the next subheading. If the problem is just a temporary bug, the following tips can help.

Sir Apfelot recommendation: Clean up your Mac hard drive with CleanMyMac Deleting installers on macOS: tips and tricks
