You've got several options:
Generate full-size STL, cut via software later
If you just have an STL, you can use software such as Meshmixer to modify it. In this case, a plain
plane cut would suffice.
Modifiy the design file
A better way is to go into the design file (in your case fusion) and modify it there. In your case, it's rather easy:
- add a construction plane
- choose the right constraints, e.g. an angle to the XZ plane or a distance to the XY plane
- choose the model
Edit > split model
- choose the construction plane you made
- rinse and repeat
If you want to get rid of parts that became superfluous after this, use the
remove option, not the
delete option, as the later tries to make sure that the object never was made in the workflow.