Fusion 360 associates itself with various file types on my computer - IGES, STEP, SAT, etc, all claim to be able to be opened by Fusion - but Fusion doesn't support opening files locally, so this is a bit of a lie.
I don't think Fusion should associate itself with any files, unless local file manipulation is/will be supported. If I double click a file and it leads to a broken experience, it's broken.
