Use an iMac as display for my Windows PC

As a running Mac, you can use Microsoft's Remote Desktop Connection software and RDC into the Windows box. Put the RDC client into full screen mode, and you can use it that way.

RDC is available from the Apple "App Store"

You could also install a VNC server on the Windows box, and either use a 3rd party VNC client (TigerVNC, or RealVNC) or you can try using macOS Screen Sharing.

If your iMac is a specific model, it may support Target Display Mode, and then you can connect it to the Windows machine via a DisplayPort cable. The Mac end would use a mini-DisplayPort plug.

https://www.lifewire.com/use-imac-as-monitor-with-target-display-mode-2260906

chrisfromglossop wrote:

Is this possible?

No it's not possible.

OK, that Specific model (Last 2009 27" iMac) does support Target Display Mode

I've actually used it on that specific model.

But between reading the question, and researching the answer, then writing up the reply, my short term memory forgets some of the details, such as the fact that a Late 2009 27" iMac supports Target Display Mode.

You're welcome.

BobHarris wrote:

If your iMac is a specific model…

A "2019 Apple iMac 27inch" is a specific model.