In my opinion, we should remind ourselves once again that we are a cartographic project and what an essential role topology and generalization plays in cartography. The reference to the segments of roads that branch off from roads of other categories has already been mentioned.
Our linear footways and crossings are abstracted networks and not an exact representation of space. I therefore consider footway=sidewalk to be wrong for these segments (and personally footway=crossing to be the most sensible variant). The exact representation of the space is only possible via area-based mapping (area:highway).
From sidewalk areas, but also from the position of the kerb nodes, it is possible to determine which (crossing) segments are above and below the curb (or on the constructed sidewalk).