The cloudbased strategy of Fusion 360 is awesome! Sometimes you still need to export your assemblies for documentation reasons or sharing stuff offline for any reason.
In Fusion you can't export an assembly with referenced parts like external assemblies/parts in the native Fusion format .f3d. Nowadays it is only possible to export these assemblies as .iges .step .sat .smt.
Fusion 360 Export in .f3d not possible with referenced assemblies/parts
Cheers
Chris