It is possible to open an STL in Fusion 360 and then convert it into a Brep format. But this creates a tessellated surface unlike the original, even if you made that design in Fusion 360 originally.
Fusion 360 could use a backwards engineering tool to sense and extrapolate what the item originally looked like before it was made into an stl. This could include checking relative surface flatness, compiling triangles into large flat surfaces, estimating chamfer angles, measuring circle diameters, even creating outline sketches derived from the solid which can then be used to drive and alter the rest of the model again.