The zone moved: « Generate » again.
Drag the zone, its white handles, or pinch and turn it with two fingers.
Real 3D: national LiDAR or official LoD2 (France, Netherlands, NRW, Switzerland). Estimated 3D elsewhere: Overture, then GHSL (90 m cells), in beige. Basic 3D: OSM heights only.
Grey volumes = real heights. Orange outline = building with no real height here.
The file is made on the phone, then « Share » opens the share sheet (Files, AirDrop, Mail…).