Yes, the Homebrew message does seem unnecessarily hostile. Not everyone can afford to buy a brand new computer every year.

I wish there were a macOS (and Homebrew) "extended support" edition with security patches for 10 years rather than 7.

Old Macs are often perfectly usable in terms of hardware, but macOS security updates have left them behind.

As of today, it's likely that the 2016 Mac I'm writing this on (which can run Monterey but not Ventura or Sonoma) is out of support.

Of course the Mac apocalypse will be when x86 support is dropped, possibly starting in the next macOS release.

Completely agree. I have two perfectly good but now unsupported 5K iMacs from 2015 and 2017 in my household, both don't get any more upgrades. Heck, I would even pay up to 100 EUR/USD for longer support. But that's probably not a viable business case for Apple anymore.

Have you explored https://github.com/dortania/OpenCore-Legacy-Patcher?

I have used it before and, in my experience and everyone else I know who has used it, the vast majority of time the newer versions run absolutely fine with no issues. Occasionally some newer features don't work, but I'd but confident that 2015/2017 iMacs would be able to run the latest version no problem.