I believe the general rule is that merchants can't charge customers more for CC payments than they do for cash payments. I assume Patreon doesn't take cash payments, so there's no issue there.
The federal ban on charging fees was lifted, but many states (including New York and California) also still outlaw this at the state level.
In addition, merchant agreements often prohibit it - for example, merchants that take American Express cannot charge fees for any transactions, even the ones that run on Visa or Mastercard.