The location of this lazaretto is marked by the remains of its walls in the scrub. As a rendering, I want the perimeter of the walls + scrub inside + the name inside: Lazaret. Is it possible? https://www.openstreetmap.org/way/674848815
It is impossible to render all features on the map you see at osm.org
You can make suggestion though on github.
Even better if you would provide a patch (or at least an icon for the changes you want to see).
For 2), knowing that the barrier=wall + name=Lazaret polygon is inside a natural=scrub polygon, without any relation, it seems that adding natural = scrub to barrier=wall + name=Lazaret gives the expected rendering. The historic key has no effect on the rendering.
For 1) I suppose that the key:historic=* has no rendering on osm.org