Again, the issue is this is an American company setting American content policy internationally.

That is not the issue. That may be the subset of the issue that you have a problem with, but the actual issue is a payment provider setting purchase restrictions period. That it is happening in the US is not uniquely bad; it would be equally bad happening anywhere else.

Storefronts and brands can set up local branches and sell through those using the local digital payment provider without getting in trouble with their headquarter’d country.

To set up and sell in that country, they then have to comply with the local payment providers. Which shouldn’t be deciding whether people can purchase something.

Censorship that happens via companies unilaterally acting on what they believe to be the government’s wishes is still censorship.