https://www.fox2detroit.com/news/total-porn-ban-proposed-michigan-lawmakers

Total porn ban proposed by Michigan lawmakers

Michigan lawmakers proposed a bill last week banning porn. This comes after the bill's primary sponsor, Rep. Josh Schriver (R-Oxford), said earlier this year that he was working to draft legislation banning all porn online.

What if the state legislature passes such a law, but it's struck down by a court (either state or federal)?

@ShankarSivarajan I don't think this edge case would come up (basically every court has agreed that restrictions on porn are not covered by the first amendment), but I'd say if it goes into effect even momentarily this question resolves yes

basically every court has agreed

That's the subject of one of he most notoriously vague court decisions:
https://wikipedia.org/wiki/I_know_it_when_I_see_it
(which was a split decision ruling that film in question was constitutionally protected)

Right now, the most likely state appears to be Oklahoma - a state legislator recently introduced a bill to do just that (tacked on to a bill that ups charges for CSAM, of course). I've put up a market for Oklahoma specifically, as well: