Responses
This one?
https://www.mangago.me/read-manga/hataraku_maousama/
Maou-sama (demon lord) is the word you're looking for though, so if you search around I think you'll find it :)
Pls help I'm trying to find a manga I can't really remember much but it starts with maybe a demon lord or something from another world was defeated by the hero I think and got reverse isekai-ed to the modern world into the body of a boy? Sorry idk what exactly happened but anything that would seem like this please lmk!!