My wife has my old 2011 27" iMac which is one of the models discontinued by Apple. It just means that she is at a limit for upgrading her OS and many of her apps won't be upgradable further. It's not a huge problem as she is able to do everything she needs to do, so we expect her intel-based iMac will still serve her well for a few more years.
I recently bought the new 24" M1 (Apple's own system on a chip SOC), which is blazing fast compared to the 27" intel iMac. I'm sure that when I upgrade again in a few years, wife will inherit my current computer (she's not much of a computer nerd so as long as she can do email, write documents, etc., she's happy) whereas I do a lot of photo and video editing and need all the speed I can get. As apple moves to their own Apple Silicon chips, support and apps for the iNtel machines will become harder and harder, but if the current system and apps you have are adequate to your needs, an old Apple computer can last a very long time.