I was distinguishing between "rating films" with "restricting access", but yeah, the content of the films doesn't matter--it's censorship whether the content is LGBT+ or Al Qaeda beheadings. The pertinent question is whether a third party is obligated to show you that content. As it relates to social media companies, my position is that if a company is exercising the right to censor (effectively to curate content) then they must also take responsibility when they curate illegal content, such as child pornography or intellectual property--they don't get to have it both ways.

Similarly, I don't think your local theater's prohibition on minors viewing 'adult' content compares favorably to a large social media company which steers and manipulates so much communication that it can unilaterally sway national elections. The latter is an issue of national sovereignty.