Places: Photon (komoot), OpenStreetMap data; the query and the map's area are sent there. Coordinates stay on this page.
Not for navigation. Positions, depths and coastlines come from open datasets of varying accuracy; depths are a coarse elevation model, not soundings.
Each layer's source, licence and resolution are behind its ⓘ in the Layers panel.
Tile requests tell each provider which area you are viewing; a hidden layer makes none.