I was wrong. You can import and scale an stl file in Fusion 360.
A little later: If you upload an stl to the cloud and open it in F360 by double-clicking, it will be 10 times the size of the original. That’s because F360 is designed around centimeters. So saving an stl to the cloud is not recommended. If you Insert Mesh and grab an STL and set the units to mm (or whatever the STL was designed in), you will get the correct measurement. You can do a Modify | Scale of an STL but you have to first turn off Capture Design History.