Reinstalling Operating System From Big Sur

If you want to install other versions of macOS then please follow these steps (How to reinstall macOS from macOS Recovery – Apple Support)

CORRECTION

Please hold command-option-r to reinstall the latest macOS compatible with your mac or shift-option-command-r to reinstall the operating system version your iMac came with.

Sorry for the confusion

I would recommend starting your iMac up in recovery mode (Steps Below) and then reinstalling macOS. This will unfortunately erase all your data (I think 🤔) but will give you back the system you had when you first received the iMac. I would then use the time machine backup to recover all your files.

Recovery Mode (and reinstall macOS)

• Shut Down Your Mac
• Press the power button and then immediately hold down the command and R keys until the apple logo appears.
• Then wait until recovery mode boots up, the background should be grey and there should be a window in the middle.
• Once the window is finished loading select your user account and enter that users password
• Then a different window should appear with four options. Select reinstall macOS and follow the instructions.

I hope this helps. If you have any other questions feel free to reply to this message.

-Person2099

I've been doing the public beta since it started. I know during the last few years if you are on a beta you cannot go back to the original or latest official release through that method unless you completely erase your drive. If you are going to try beta for the first time or have issues with having to have certain software which may not be operational on Beta or you aren't sure how to troubleshoot if there is a problem and eventually there will be. BE SURE YOU BACK UP YOUR DRIVE BEFORE INSTALLING THE BETA (sorry for the caps). Hope that helps. I haven't bothered with the Communities for a long time so hopefully I haven't stepped on any toes.