They may not have realized it, but until UEFI-only computers started becoming common, people mostly were still effectively drawing the line at IBM compatibility

What's the fundamental difference between an Intel Macbook and my old 2018 Lenovo laptop? Either of them can run modern Windows, Linux, whatever. For most modern uses, they're basically equivalent. The one thing that makes the Lenovo different though is its firmware. The Lenovo has BIOS support and the Mac doesn't.

If you then add my current Framework laptop, which is UEFI-only, to the comparison though, it gets kind of fuzzy. It's clearly not a Mac, but what is there to really define it as a PC? It can't run MacOS, but that doesn't really work to separate it because plenty of PCs can run MacOS. It's not made by Apple, but if that's all it takes then is a Chromebook or one of the Talos POWER workstations a PC too? It's kind of hard to say the Framework is a PC without including so many other things that the term PC kind of loses all meaning.

I think the term PC has just outlived its usefulness and we need to move on to saying more specific things than that to describe computers. In most modern contexts, all that matters is what architecture a computer is and what operating systems will run on it, and PC just isn't really a great term to convey that information anymore.