it's very possible that some ~30 year old CPU wouldn't offer correct instruction sets to run a modern OS, so yes.I heard that operating systems must be compatible with the CPU in order to work. Is this true? I have never heard of such a thing.
just as without proper security protocols many older systems cannot run Windows 11.
but in the reverse it's also possible.
if the OS doesn't provide any, and you cannot find your own, proper drivers to allow an older OS to function then you may be in a similar bind.