It's great for documents, etc., but I would use something different for photos. Check out Immich and PhotoPrism. I prefer Immich, because it has official mobile apps for Android and iOS. PhotoPrism has an unofficial gallery app for Android, but it doesn't have sync capabilities. For that, you would need to use a 3rd-party, closed source app called PhotoSync. I think Immich is just the better option.
Btw it wouldn't even matter, since the encryption happens in the client app. The server basically just passes around encrypted pieces of data between devices.
Also, just think about it: The CCP loves spreading propaganda. There's a massive social media platform controlled by China, which is used by young people in foreign adversary nations. Why wouldn't they leverage this platform to spread their lies and influence people? It's literally the perfect opportunity.
Then perhaps use a firewall like NetGuard in whitelist mode, to only allow selected apps to access the internet
As an additional layer of security, you can use NextDNS with the No Google blocklist, and block all connections to Google servers in DNS. If you need to access specific things like YouTube, you can whitelist them.
You mean Bazzite? Yeah, it's really great. Based on uBlue, which is actually based on Fedora's Atomic spins. It's very stable, secure and reliable, and pretty hard to mess up. Basically the closest thing to SteamOS that you can get.
uBlue Bazzite is pretty cool, Fedora/Nobara, Pop!_OS, Mint, etc. mostly just work, Gauda is arch-based, is optimized for gaming and performance and is pretty user friendly.
Or Universal Blue in general. They also make Aurora and Bluefin, both are amazing!