Do you think Every Door is a good way to do that? Is this [1] wiki the right place to look for the data model/tag guidance you are talking about?
I heavily suggest to switch to https://organicmaps.app/, which is a maintained fork of Maps.me, without user tracking and the whole wallet shenanigans.
You can just enter an amenity:bench poi, but it's useful to include additional information in tags. StreetComplete, for example, has a quest that adds the backrest information.
Osmand lets you add pois, but offers little guidance which tags are appropriate for which kind of poi. Every door seems a bit more helpful in that regard.