Polygon in Overpass-turbo

I am collecting and making so called Points Of Interest from several places in Western Europe.
These Points (POI) are available for all kind of people traveling (by bike or foot).

If people are asking me for a specific number of POI (from OSM) on there route I would like to select these POI by using overpass-turbo and the instrument of polygon to select the area where the route is.
e.g. The track starts at Maastricht and is finishing in Basel.
What kind of actions I have to do to be succesfull to make multipoint polygons as a selectionitem in overpass-turbo to get the desired objects from OSM?

I know how to make use of the overpass-turbo option for making ‘square’-polygons but I can’t find an option to make ‘selfmade’-polygons as a selectionitem in overpass-turbo. All suggestions will be helpfull.

overpass turbo has no built-in support for this use case, i.e. you need to calculate the polygon on your own, and use the resulting list of lat/lon pairs for the (poly: ) filter (see Overpass QL documentation how this works).

Maybe you also want to read mmd's Diary | Download along my own virtual way in Overpass API | OpenStreetMap for some alternative ideas without creating a polygon on your own.