This is nonsense there are basically two popular OS families (Windows and UNIX-like) and both are able to run software for the other (wine and WSL).
Neither is macOS/iOS written in Objective-C as claimed, its written mostly in C with a little asm (like all UNIX-like systems) with a driver subsystem ioKIT written in C++.
Just because something dates from the 70s and is “old” doesn’t mean its “obsolete”. It can also be basically “done right”. I don’t think there has been much progress in OS design recently, although things like capabilities and micro-kernels are interesting and there have been developments with new file-systems.
Good point about main two having compatibility layers. Far as OS design, there’s always progress happening in CompSci and FOSS. There’s just rarely any attempt to port whatever they come up with into mainstream OS’s or make it a mainstream OS. It can take a lot of work to do that. GenodeOS and MirageOS are possibly only ones I’ve seen with really-different architecture that got deployed, developed a serious community, and are still developed.