What are some actual anime you would recommend to a fan of western animesque "adult" cartoons like Castlevania, Legend of Vox Machina and Arcane?

Studio Trigger is pretty well known for taking inspiration from western animation. Panty and Stocking, BNA, Dungeon Meshi, and Edgerunners are obvious ones. Idk what you mean by "actual anime" but you should probably just look at https://myanimelist.net/topanime.php and click on anything that looks interesting. Considering you liked Castlevania and that Critical Roll show your standards can't possibly be very high.

Bump

Watch Baccano.