Is censorship of transactions actually possible? How would that work?

Please forgive my ignorance. All of a sudden, there seems to be a lot of concern about how the U.S. government might be able to censor transactions via U.S. validators. I would like to understand how that would work.

In PoW, such censorship would only be possible with 51% of the hash rate because even if some miners refuse to confirm transactions in their blocks, they can't prevent the other miners from confirming them in theirs.

Is PoS different? If some of the validators refuse to confirm transactions in their blocks, then couldn't the other validators confirm them in theirs?

TIA.