theres subscribestar, and buymeacoffee, and go figure, onlyfans which isnt just human content but also for content creaters of all kinds. one subscription could get you a link for a discord channel to download it. i think discord and onlyfans can be integrated together. it just takes the right bot that can check the api of both, which isnt so far fetched. other than that, theres lots of sites that do exactly that.
lots of sites have "visit our discord to see instructions on paying for and downloading the game" they just set up a bot or something. i know guys who have used twitch bots that raise your discord status of different tiers, if you donate on their twitch page, and the higher tiers have the downloads. only problem with that, is needing them to have a user submitted role (they can click to attain) for 18+ role. then you just have the 18+ role along with an appropriate donation role be allowed access to a channel with the downloads. kinda simple.
the issue with it is that donators automatically get the game, and people who have only paid on discord might not feel as incentived to donate to your twitch.