@Richard You mean also merging nearby polygons where the gaps are not really visible on the given zoom level, right?
Currently, it doesn’t look like vector.osm.org does any geometry simplification (neither merging polygons nor simplifying geometry).
The below is the boundary of Schaffhausen at the German/Swiss border on zoom level 5 or something - zoomed in while preventing MapLibre from loading any new tiles adequate for the zoomed-in map (e.g. by going offline and having no cache).
And this is how it looks at the adequate zoom level. (The line thickness is the same, it just appears thicker because those are actually micro-zigzag-lines as if drawn with a trembling hand)
