Hm... I agree that Instagram is not a neutral source. I also agree that there are going to be some biases imposed by the user base.
I don't believe the US government plays a major role in Meta's content moderation behavior. Meta if anything has shown a reluctance towards any political or news content in recent years. That's not to say the US government doesn't have influence but their influence is (from what I've seen) oriented around fighting disinformation and threats of violence ... not cherry-picking the discussion of subject matter. I think there would've been a pretty significant leak out of Meta by now if there really was a strong political bias or government influence in content moderation.
I don't think any of these lines particularly fall along political lines within the US either. There are people on the left and right taking different sides on virtually all of the topics with statistical divergence; many of them are unusually bipartisan within the US.