iMac as an external monitor

Hello, welcome to the Apple Users Community.

It's an educated guess but I would say yes.

Your system is 10.11 El Capitan, yes? First released in 2015, if you haven't upgraded since then, I'm going to say you have an iMac older than 5 or 6 years which means it's not going to be an issue at all.

I could be wrong, which happens a lot but I'm going to take a flyer on this one and say you should look at this link

https://support.apple.com/en-us/HT204592

Best of luck

[Link Edited by Moderator]

See the link below for information as to what models will work and how to proceed.

https://support.apple.com/en-us/HT204592

Your 2012 iMac should work with the proper adapters.

If your iMac is late 2014 or later then no.

Not possible with any Windows based PC. Never has been. I wish you would have explained that at the beginning.