No, Itch.io doesn't have a subscription model. It's more designed for one-time purchases or donations.
Regarding the adult content rules, you can review them here:
https://itch.io/docs/creators/faq#is-adult-content-allowed
Be aware that Itch allows more things than some of the payment processing companies allow. If you're going to charge for that content, you must also comply with the limits set by companies like PayPal.
If you plan to collect money for your content, then you must adhere to the acceptable use policy of all the respective payment processors that your account utilizes: