Someone needs to seriously create a solid off-cloud personal computing experience. Phones that don't record everything and sell it. How about all these laid off software engineers? Can you guys start something?
There is not one only solution for off-cloud computing, but there are solutions for different services. For photo and video storage instead of Google photo etc you may give a try to Immich.app, surely more suited for this job than Syncthing...
Google and Apple protect themselves against this by not allowing other apps to use these APIs on the OS . I think there are a lot of talented devs trying to make this work