Samsung and others OEMs have little incentive to collaborate with privacy-oriented roms because a large part of their business models depend on the surveillance baked into their technology. They’re only interested in security as far as it frees them from liability, or can be used as worthwhile PR. They might not be based out of the US or China, but they do still operate in said countries and are all too happy to comply with data or unlock requests.
Honestly the only drawback is if you don’t already do selfhosting, NextCloud is kind of a big undertaking. If you’re already familiar with containerization and networking basics, it’s very smooth.