Maybe this can help ? https://anyconv.com/f3d-converter/
For convert a .f3D file

Not yet tested!

Curious : Tested ! Says only STL in the Head of a Popup Menu but infinite waiting for a simple cube.f3d !
So don't works for the moment!
Try other writing STEP in the top Menu : same result! :)

Tryed with an OBJ file - big list of possible convertions : but same no result!
OBJ to STL YES
OBJ to STP (who is in the PopUp Menu of the OBJ file) NO ! :(