How to use an iMac as display for Apple Mac mini with M4 Chip

As mentioned you cannot. Please remember iMacs are computers they are NOT external displays for other devices. For your new MM, please simply buy an external monitor, why...simple:

• Inexpensive external monitors start as less than $100. However for a very nice display expect to spend about $300.
• No expensive cabling necessary.
• Simple connection
• Dead Reliable

That will not work, because none of the Mac's made after 2019 support using an iMac as a display in Target Display Mode.

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

You will need to use an after-market display or a studio display with the new Mac mini.

see > Connect a display to Mac mini - Apple Support