Restart your Mac and immediately hold to enter Recovery Mode. Select Disk Utility .
As a last resort, if you're dealing with extremely sensitive data or an old hard drive that's no longer usable, consider physically destroying the hard drive. This can be done by: how to wipe a hard drive
Deauthorize apps like iTunes, Adobe Creative Cloud, or Microsoft 365 that have "device limits." Restart your Mac and immediately hold to enter Recovery Mode