Batocera is nice too. It’s half an emulation console and half Kodi. You can tell it to launch Kodi as default too. Whereas LibreElec is only Kodi with a limited gaming ability

No. Just install GrapheneOS for free yourself

You have plenty of good information regarding gaming already so as far as Adobe Lightroom goes, try Darktable. It’s a FOSS alternative and very nice software

Ontop of the various good suggestions already mentioned you could also keep your choice of medium in a safe

Good luck with privacy there. At minimum disable the AI stuff that has access to every app, and that’s if you believe their toggles do anything, which Apple has been proven to not listen to them in the past