> if a big tech would create a map of publicly available toilets

You don't need big tech for this: OpenStreetMap [1], a map (actually, a database) that works like Wikipedia, is there for all of us :-)

It has information about public restrooms, whether they are accessible, gratis, and toilets are only a very small part of OSM.

The more people contribute, the more awesome it becomes.

A sibling mentioned Organic Maps, it's one of the many apps out there to conveniently use OSM (and contribute).

[1] https://www.openstreetmap.org/