Transfer or Reset IMac

The following if from the document that I linked to:

 Erase your Mac

1. 1. Shut down your Mac.
   2. Start up from macOS Recovery, then use Disk Utility to erase your Mac. For details, follow the steps to use Disk Utility to erase your Mac.
   3. When done, quit Disk Utility but don't restart your Mac.

7. Reinstall macOS

1. 1. While still in macOS Recovery, choose Reinstall macOS, then follow the onscreen instructions. Learn more about reinstalling macOS from macOS Recovery. 
   2. After reinstalling macOS, your Mac restarts to a setup assistant. Press Command-Q to shut down instead of continuing setup.

That's how to do it.

To use " Erase All Content and Setting "

" This process, known as Erase All Content and Settings, requires internet access and can take some time; however, it helps ensure that your device can be accessed only by you."

1. Do one of the following:

• • On your Mac running macOS 13 or later: Choose Apple menu  > System Settings, click General , click Transfer or Reset, then click Erase All Content and Settings.
  • On your Mac running macOS 12 or earlier: Choose Apple menu  > System Preferences, then in the menu bar, choose System Preferences > Erase All Content and Settings.

1. In Erase Assistant, enter your administrator information (the password you use to log in to your Mac).
2. Review items that will be removed in addition to your content and settings.
3. On your Mac running multiple user accounts, click the arrow next to your account name to review the items.
4. Click Continue, then follow the onscreen instructions.

From what I see in your above image is this computer belongs to a Family Account

Did you follow the instructions in this Apple document: What to do before you sell, give away, or trade in your Mac - Apple Support?