Replacing Apple with a more privacy-preserving alternative is not really about UI minutia. UI/UX is mostly solved, for 2D displays at least. Gnome, KDE, Elementary OS's Pantheon, and others all offer usable and customizable variations on this tech that get you 90% of the way to Apple's standard. Incremental improvements in 2D UI/UX are reaching a point of diminishing returns, where it's more annoying for users to have to learn new interaction mechanics than to simply stick with the ones they know, even if the new mechanics are slightly better in some way.
Rather, I think the area that really needs focused developer attention, and with bigger and more meaningful payoffs, is in bringing the most secure and hardened base systems up to full compatibility with the broadest possible application ecosystem/s. The best option for that right now appears to be Linux + Wine/Proton, ideally using a hardened Linux base like Qubes or SEL4 or similar and Nix/Guix-like reproducible builds, while integrating the extensive work already put into existing UI/UX/DE's. I think if hackers want to achieve this objective, then that's where they need to start and build a community around.