The question is the extent of the limitation. And what’s “reasonable.”
Instagram offers what they offer. A forum for a topic or a medium offers something to you. The fact that they’ve chosen not to offer other things isn’t a limitation on your expression, any more than my burger shop is for not selling salads.
We don't owe Instagram some sort of being nice or saying nice things. If they run a subpar business that punishes freedom of expression, we can call that out and say it sucks.
But it's absolute baloney to claim that they punish freedom of expression because the venn diagram of "content they're willing to host on their infrastructure" and "content you want to publish" aren't perfectly aligned. Calling my burger shop bad because it doesn't serve salads is similarly baloney.
Being a private entity that allows users to express themselves isn’t a restriction on the types of expression you don’t allow. The default is that Instagram doesn’t exist, not that it exists and must all anything you want it to.