the tags that definitely mean explicit sexual content
All tags have a fuzzy meaning that lies in the eye of the beholder. That is not only an issue with adult tags, but for tags on itch in general, since the developer choses the tags.
Also, just because you tag a thing, does not mean you will show it in graphic detail. It is debateable, if pure text games should be considered "nsfw", even if they deal with such topics and thus could tag them. But even with graphics, you can have topics without showing them. There is a reason why you used the explicit qualifier.
Also, the current tag descriptions do not even spell out that it is explicit content, for example this one
Erotic
Usually containing sexual themes, content or more. Not safe for work most of the time.
Which tags ignore the setting is arbitrary. But it is not tags you typically find on games aimed at underaged players. Except horror maybe. But that is another discussion, how much horror a game can have before it has to be marked as adult. (the horror tag does not ignore the setting, but by the logic for the mechanism, it should).