Mac Studio--- iMac

If you want to certain old iMacs as a display, that feature is supported through Macs that shipped in 2019. Later models AND more recent MacOS are not supported, so Apple-Silicon Macs do not support it.

Read VERY carefully, the article is extremely information dense:

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

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Define "connect".

You can use the iMac as a hard drive using Target Disk Mode: link->

You can use the iMac as a screen using AirPlay to Mac->Set up your Mac to be an AirPlay receiver - Apple Support

But you will need an actual monitor to set this up.