I started learning Unity, but when things weren't working as I expected I went "old school". DEMS and satellite overlay into TG. Micro exporter and render layers out to OBJ, PoseRay to set UV and add material and then upload to Sketchfab.
https://skfb.ly/6sBwN Just a quick test from Glacier National Park (USGS 10m NED)
I used the "Diffuse before lighting" render layer for the texture and it's a nicer texture than using the original imagery (Exposure/gamma conversion from EXR to 8bit in Photoshop). It may be clunky but I like the result. Will have to make up some HDR backgrounds fro Sketchfab.