If you mean those ro.product.*, ro.system.*, ro.vendor.*, etc. and some other device identifiers, I think you can adjust many of them when compiling GrapheneOS yourself, which, however, requires a lot of storage and computational resources. If you mean the user agent HTTP header (and navigator object), there’s no such thing as a system wise UA since UA is to recognize the OS and browser combination, and the UA header can be spoofed with those user agent switcher extensions or, if you are advanced user and want fine control, Header Editor, which can be added to Android Firefox by visiting it with desktop enabled.

https://video.hardlimit.com/

I’m a Taiwanese and interacted with a bunch of Linux users from Mainland China on Mastodon. From what I saw, I don’t think it’s as easy to use Linux in China, mainly due to the Great Firewall. They often need to tweak the mirrors and even tunnel through their VPS overseas.

I think limiting from the platform is not a good option. For some teens with a horrible family (domestic violence for example), social media maybe the only shelter they could turn to. Also, those companies tend to break open web and require an account and even verification in the name of protecting child. DNS blacklist enforced by parents is probably a better option IMO.