iMAC will reset to factory

Unless this computer is listed as per below, that features is not available

Use Erase All Content and Settings

This feature requires macOS Monterey or later and a Mac with Apple silicon or the Apple T2 Security Chip. 

If this machine is an older Intel machine >>

Follow the direction from below link >>

You may not be selling or giving the computer away, but the outcome will work for Resetting to Factory Setting

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support (CA)

Have you looked at this Apple Support article? Erase your Mac and reset it to factory settings - Apple Support

Hope this helps.