Hi, I just found some asset packs where their creators don't mind to be included in adult-orientated games.
Maaot and Kauzz
Maaot's work and sample,
https://maaot.itch.io/mossy-cavern
https://maaot.itch.io/2d-browncave-assets
Kauzz's work and sample,
https://kauzz.itch.io/pixel-valley-plataform-tiles -forest and cave
https://kauzz.itch.io/kpf -forest
https://kauzz.itch.io/kpwf -winter forest
https://kauzz.itch.io/kpc -cave
Permissions from Maaot and Kauzz to use it on adult games
You can use these assets in any projects as art reference, or modify it to suit in your projects.
Good luck 👍