Can I connect my laptop (PC) to an iMAC 24" M1 and use it as a monitor

As others wrote the answer is no.

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

It's no substitute for TDM but you can use Screen Sharing: Share the screen of another Mac - Apple Support.

Wow. Surprised to see the response is "No."

The iMac has a monitor. Would be more utilitarian if we could use the screen with out laptop.

I have an old iMac as well and when Phill asked the question I thought it was a neat idea.

Understood, we get your question daily sometimes many times during the day. Apple makes external displays albeit very expensive for your needs. Target Display Mode was never intended as an Apple feature. Back in late 2009 some intrepid PC users found a way for Target Display Mode to work on late 2009 27" iMacs and some early 2010 27" models. However it was really a fluke and never worked very well. As mentioned if you need an external display, please buy one. You will find them not expensive and far more reliable. Another option is to look for third party solutions such as Luna display but IMHO that is expensive and not an elegant solution at all.

No.

+1 No that will not work. Macs are computers, they are NOT external displays for other devices. If the PC needs an external display, please buy one.