will apple stop supporting iMac 21.5 inch mid 2014 imac

Your 2014 iMac is already classified as "obsolete" by Apple.

You will get no support from them.

You might, however, sweet talk an Apple Authorized Service Provide (AASP) into assisting, but that would be a case by case basis and depend on what sort of help you are seeking.

Maybe there is something we here in the Communities can help you with?

By the way, your 2014 iMac should be able to run up to macOS 11 Big Sur, but nothing newer.

And the Big Sur OS does continue to be supported with updates at this time.

You’re welcome. 🙂

Yes, many have discovered that Big Sur and newer OS versions don’t particularly like to run from older HDDs. The SSD makes a big difference in performance.

Enjoy.