If a Mac is being used to build software targeting apple platforms it needs to be running an up to date version of MacOS.
On this point, I will concur entirely; if you're using XCode for professional software development purposes, you clearly would be better off with an up-to-date system, both in terms of hardware and software. However, I don't think that necessarily applies to OP's use case of "office/web/streaming stuff". For that type of light use, any recent-ish computer (and likewise almost any operating system -- depending upon what "office" means) will likely suffice. It also doesn't apply to my own use case, which is primarily gaming and relaxing. Regrettably, I must live in a "Windows world" in my professional life, as do many others here, no doubt.
Running the latest version of Windows on a Mac is not supported either ...
Technically true -- but as many users of older Macs will happily tell you, "not
(officially) supported" doesn't always mean "not able to run." A subset of Mac owners have made a practice for many years of shoehorning newer versions of macOS onto older "unsupported" Macs, in order to squeeze a little bit more life out of a perfectly serviceable piece of hardware. It's not always easy, but it is doable in many cases. Similarly, my 2019 iMac presently has Windows 11 running via bootcamp, without a hitch.*
... and Windows 10 will probably be out of support before the last Intel version of MacOS.
On that point, I'm not sure that I agree with you. Microsoft has backed themselves into a particularly thorny corner. By artificially limiting the officially supported hardware to such a small subset of the existing install-base of Windows 10 users, they have guaranteed that there will still be a not-insignificant Windows 10 userbase well beyond the official end-of-life date for Windows 10, which is (currently) October 14, 2025, according to
Microsoft.
So will they just summarily stop issuing all updates for Windows 10 on that date? Not very likely. In fact, I don't even think we have to speculate; we can look at history. They've bumped up against this issue on multiple occasions in the past with older Windows releases; as long as there is a significant userbase, Microsoft is essentially forced by their own previous success to continue supporting those users with
at least security updates, for longer than they would prefer. Although, who knows? Maybe instead they'll just cave in, and relax the hardware requirements for Windows 11 to try to migrate more of the legacy W10 users over to W11. (I know; it's not very likely... but weirder things have happened.)
* But no: For now, I would not bother to repeat the Windows 11 upgrade for any computer -- even if it's fully supported -- as long as Windows 10 is still able to work fine on it. In my opinion, while W11 generally works well enough, it brings nothing at all of actual value to the table that isn't already available in W10. (Literally. Absolutely nothing. Nada. Zilch.)