This is quite odd and I have lost too much time at this point.
I have a simple line in a scene: https://panda.maps.arcgis.com/home/item.html?id=becd3652c526486098d6f5bb989ec540
I want to make an app that animates the rotation of the earth with my simple line on it.
I create the scene:

but when I create a web app using the 3D visualization theme it seems it will only show my line as a weird protruding column?? or a floating dot? Polygon extrusion makes it disappear. What the..???

no other application templates have the rotation option? this seems really weird...it's just a single line!
https://panda.maps.arcgis.com/home/item.html?id=4452e127f664493bbc4c945195cee16c