Does anyone know if it's possible to open a project template (.aptx) using ArcPy? Opening using arcpy.mp.ArcGISProject() doesn't appear to work and I can't see any way of creating a aprx off an aptx using ArcPy.
Alphabetical list of arcpy.mp classes—ArcGIS Pro | Documentation
As you found, you can access a project but not through a template
you can access tools through arctoolbox that perform that function
Extract Package (Data Management)—ArcGIS Pro | Documentation
see the code sample