Steam chose to not offer adult games on the German market for the time being, because of age verification issues of the buyers. I am not sure if such games are available via GoG. Stores that are not actually in the German market usually work. Like Itch. Or Nutaku.
They are into micro transaction games with their virtual currency. But they also sell regular adult games. You will find some games that are here on Itch and on Nutaku. But not all that many. And they do not seem to have early access games atm.
