I want to reinstall catalina on my Mac because the latest version off Big Sur 11.6.6 is full of bugs

robert_coady wrote:

how do you reinstall

Erase everything, and start over. You can manually pick over files from a copy of or backup of your old install and see if they’ll work in the older environment—many but not all will—but there is no automated downgrade. Not without restoring a pre-upgrade backup. It’s manual.

Erase and reinstall macOS - Apple Support

I’d boot Recovery, and try a repair there using Disk Utility, and see if that clears whatever happened. This assuming there’s no backup to restore from immediately before the occurrence of the error.

Intro to macOS Recovery - Apple Support

How to repair a Mac disk with Disk Utility - Apple Support

Your footer here shows El Capitan 10.11. you’re discussing Big Sur 11 and Catalina 10.15. Monterey 12 is current. Downgrades are harder than upgrades. if Disk Utility repair from Recovery cannot resolve this, I’d try either a re-install and a migration, or installing a newer version and with migration. Not a downgrade.

Download Catalina from the link you referenced at the top of this post.

Create a Bootable installer from that download

Back up your Mac.

You will likely not be able to Migrate your Libraries, so you may want to export all of the Photos, Music, Contacts, etc. from any apps you use to an external drive. You may have to use that to import them back into Catalina's programs.

Boot from the Bootable Installer

Open Disk Utility

Erase your Mac. You have to "Show All Devices" from the View popup menu in Disk Utility, select the internal drive device, and Erase. I would suggest starting with APFS as the format. If the install can't find the drive, erase again as Mac OS Extended.

How to reinstall macOS - Apple Support

You can try Migrating from your Time Machine backup in the Startup Assistant, but as I mentioned, I'm not sure if it will work.

I give you my permission.

what does this mean?

You said you want to reinstall Catalina. Go ahead.