Is it not true that when entering the US you are required to show all your social media content on request, and if there is anything negative about the current administration, you can be denied entry (if you are lucky, and not detained for an indefinite amount of time)?

Truly exceptional indeed. You are basically on par with China.

Do they really do that and what do they do when you say you don't have one? Do they believe you or not having one is as suspicious as having one with the content they don't like?

FWIW, you don't have to do any of that to enter China.