> Are there open and privacy-preserving standards that can solve the problem of bots and minors? If not, what would be required to establish one, and is it realistic?

Ideally there shouldn't be standards for this. What we have already is enough.

Companies claiming they are closing down their services/devices to protect the users is total BS. Facebook has admitted they get 10% of their ad revenue from scams, and that's the reason they won't go after scammers on their platforms.

Same can be said for Google. They could come up with numerous ways to block bots or make captchas harder for actual bots (while also not flagging every non-Chrome user as a potential bot, like they do nowadays), but they pretend this is an unsolvable problem that requires a nuclear solution, it used to be Web DRM but now it's called Fraud Defense.