There is a standard: https://en.wikipedia.org/wiki/Geo_URI_scheme

I have it working on my Android phone. It's clickable links that open my map app of choice (or rather a selection dialog).

It's just that the big players do not want to use it.

I'm a bit surprised this doesn't have more traction. It doesn't seem to have been designed with POIs in mind, which is unfortunately a limitation.