iMac as display for Mac Mini M2

Unfortunately, that setup is not supported by Apple. The iMac cannot be used as a monitor for any of the newest Macs and Target Display mode is no longer a feature of macOS, having been deprecated several years ago.

Please see: Use your iMac as a display with target display mode - Apple Support

Per the link above:

• Your target iMac (monitor) must be using macOS High Sierra 10.13.6 or earlier. 

• In all cases the source Mac that you're connecting FROM must have been introduced in 2019 or earlier and have macOS 10.15 Catalina or earlier installed.

However, you might consider a third-party solution, for example: Luna Display or Duet Display.

No sorry, a new Mac mini does not support using an iMac as a display in Target Display Mode.

see > Use your iMac as a display with target display mode - Apple Support

If you get or have a new Mac mini, then you will need an external display.

see > Connect a display to Mac mini - Apple Support

You're welcome.

All is not lost. Shop around. You may find a 24" or larger monitor to go with a new Mac mini for less than the cost of an iMac. It's definitely doable.