I recently made a self-hostable web app* that works the same way; the user downloads regions with a point and click, I have the data on S3. I used Protomaps, which is vector library for the browser. I did look into seeing if I could just download the maps straight from Protomaps. I didn't end up doing so, I think it's because they didn't seem to have an API that I felt like I could scrape wholesale.
But also, it turns out that there's a question of how that data is generated. There's a certain schema of what sorts of things show up in the browser, perhaps with styles giving options for how to display them. But which raw OSM data you decide to include, and which visual element it corresponds to, is up to the producer of that data. So thinking of Organic Maps and OsmAnd, I bet they choose slighly different things and probably change it over time.
But also, it turns out that there's a question of how that data is generated. There's a certain schema of what sorts of things show up in the browser, perhaps with styles giving options for how to display them. But which raw OSM data you decide to include, and which visual element it corresponds to, is up to the producer of that data. So thinking of Organic Maps and OsmAnd, I bet they choose slighly different things and probably change it over time.
* https://sandstorm.org/news/2023-12-05-osm-on-sandstorm