Earlier quoted context omitted.
Yeah, that’s the downside to swapping architectures. x86 goes to great pains to be backward-compatible at the instruction level, and then MS puts a lot of effort into keeping Windows backwards compatible. A couple years back on Windows 10 I successfully installed and used a PCB layout tool from 1998. I was shocked at how smooth it went. I think it needed to run as administrator but otherwise zero issues.
Windows NT has run on multiple architectures since day one with x86/PowerPC/Alpha/MIPS flavours, however x86/AMD64 has won over them. Trying to add ARM desktop to the mix hasn't indeed been easy, because of backwards compatibility efforts, most folks don't care about Windows ARM laptops. Pocket PC/Windows CE also had ARM/MIPS variants.
True in theory, but in practice you're not going to take a Windows NT PPC .exe and run it anywhere today. Apple's done a decent job with Rosetta and Rosetta 2 doing CPU emulation when doing the transitions but I don't think they've ever targeted the same "You can run Windows 95 x86 .exes on Windows 11 x86-64" backwards-compatibility goal.
My experience with OSX and iOS backwards compatibility is similar to the post author's: things might break once in a while on a long timeframe but it's usually pretty easy to rebuild for a newer version. This works fine so long as the company that owns the source code actually still exists and is willing to build a new version.