You cannot let or forbid a 16yo to use stuff. You can only decide whether they will do it in the open or in hiding. Personally I'd rather have them talk to me about it than hide it from me.
I'm still confused why people are so hell bent on using a single window exclusively. It's a natural way to group the tabs and it was there from day one!
The only thing we know without a proof is that they might be doing it. We don't have a proof they do it but we also don't have any proof they are incapable of doing so. A reasonable course of action would be to take precautions against it while not condemning them either, until they are either proven actually guilty or actively unwilling to up their security, which would also strongly imply the former.
Until it's proven the data is E2E encrypted, it's a fair assumption it can be read by a 3rd party, either now or in the future. E2EE is the only proof that matters, everything else is just a corporate "trust me bro".
I'm sure we can compromise on a mandatory database of registered AI-generated content that only the corporations can read from but everyone using AI-generated content is required by law to write to, with hefty fines (but only for regular people).
The same could be said about any game with any non-Steam availability. I don't think that was OP's intent. That being said, emulators surely were not the intent either.