The Amiga build of Firefox did exactly that. All the platform specific stuff was in separate files (supposedly) so as to not trigger the per-file disclosure rules.

Now, "modern" Amiga is a horrible dumpster fire of a software development and community. It's a worked example of that saying about how people fight most fiercely over the smallest stakes, with no more than a few thousand users fighting over which of half a dozen ways forward "must" succeed and a long history of scams, etcetera.

But that's your example, such as it is.