A modern PC can most certainly run Flight Simulator. Most PCs still have an EFI that provides a CSM. And most GPUs default to running a program that provides VGA (and thus CGA) compatibility.

What's even more surprising is that it functions properly, other than a timing issue with the World War I Ace mode.

If you want to run FS 2.11 or earlier, you will need to get a cracked copy, since its copy protection requires using a diskette version. But "PC compatible" has never required diskette drives - the original IBM PC included an edition with no diskette drives at all.

(I'm personally more on your side of the argument than not, but need to point out literal details of the "standard" that is under dispute)

the article says if we transported back to the early 80's people would have said "it doesn't run Flight Simulator", so what that would have meant?

the original Flight Simulator for the IBM PC--first independently produced, then purchased by Microsoft--booted itself directly from the floppy; meaning, you had to reboot in order to run it; and it had its own "custom operating system" or really no operating system at all, something more like a kernel, or just an app.

yes modern "PC compatibles" do have some means of running that old software, but it won't work out of the box atm.

On the Intel side of things, Skylake retired VGA support.

Modern UEFI implementations do not universally support BIOS, which means things like https://github.com/FlyGoat/csmwrap are required.

Also, timing problems are a major reason for the transition to "WinTel" rather than PC-compatible... along with things like 8bit ISA support.