That's actually good news I wasn't aware of. I have a couple Macs (a MacBook and an iMac) that I mostly just use for browsing. As long as they get security updates I'm pretty well set.
I probably will replace the iMac with a Mac Mini at some point but this means there's no rush.
And even after they go out of official support there are people who figure out how to run the latest or at least later software on them, depending on what you use them for.
And of course, with the Intel ones you could install Linux or even Windows.
Mostly just browsing. All my multimedia, code stuff, and other essentials are on an M1 MacBook. I could probably run nothing but a browser if I wanted to clean up the systems. So basically I can keep running them for a long time. They're fine for their current purpose.
I probably will replace the iMac with a Mac Mini at some point but this means there's no rush.