Do they make money by showing ads to people who are able to actually get to their website?

Increasingly, no.

Musk had shown over the last year or so that he clearly has no idea how the web or websites work and probably thinks all those links will be magically updated because everyone loves him and wants to make his vision of stupidity be reality and will go and fix them.

Ostensibly, although many (most?) of Musk's actions since the takeover have been rather detrimental to this goal.

That didn’t stop them from limiting the number of tweets users could browse to a tiny number.

Again. Do they care?