No legal fiction is inured to the machinations of its host state.
Social media companies have also their own nefarious goals so you don't have only to worry about your government but also about the (un)intended consequences of attention capitalism
Countries other than the USA have agency and interests, and are entirely capable of seeking to influence your thoughts and actions to affect change if it furthers their goals (it is literally an election year).
This isn't mutually exclusive to being concerned about the US government actions in this space but the risks are completely different.
There are alternatives out there which I hope still deliver on the promise of allowing secure communications, and we're free to roll our own, but I strongly suspect that the US gov will move in on anything that gains enough of a following.
I think that we're still far better off than the Chinese, but we're not as free as we pretend that we are.