This is an extreme exaggeration. If you've used Twitter since the Musk takeover and come away with the impression that you can't criticize him there, you've had a completely alien experience to mine- it seems to be the main use of the site these days.
He has banned parody accounts that don't specify 'parody' in the username, he's threatened to de-amplify negative tweets, and he's banned the ElonJet account. I vehemently disagree with all of those moves, but the idea that the site is now unusable to say anything that he doesn't like is absolutely hyperbole.
This includes criticizing him in various ways.
Say what you will about pre-Elon Twitter; I never heard about anyone getting their account banned for saying bad things about Dorsey.