I have to say that I have seen this type of censorship with my own eyes in two ways
They have way more techniques than the obvious ones.
How many times does a video not load on Twitter? How many times when it happens to be a conservative leaning one? How come it never happens with a democratic leaning one ... ever?
In the past I've dealt with persistent troublemakers by showing an error message as though the site was down. If I can think of it, these companies can.