Patreon or Subscribestar right now. If the page gets taken down then there isn't much we can do to honor early access purchases unfortunately.
Do you not know who your paid Itch subscribers are?
From what I've read, it won't be sufficient for Itch to de-index adult content. They and others will eventually be forced to remove adult content in order to continue to be able to receive payments.
Even if Europe and others develop a new payment system independent from the US based companies, it will be hard, probably impractical and possibly impossible for a US business to use it.