If you really want to jump through all the hoops just do a search for "Download Windows 7 ISO, Legally and for Free" - and yes, it is legal and free. I actually did this a while back because I needed to test some windows-only software one time. But when it came time to start learning 3D CAD I went with OnShape because it's just a whole lot easier - launches immediately in the browser and I can easily have multiple windows open on multiple monitors.
Having said that, I think that Fusion 360 is the more mature software compared to OnShape, and has a bit more functionality. But at my level, the differences are inconsequential and not worth the hassle of running another VM. I routinely use VMs to try out complex software so I don't have to worry about messing up my working computer, but every VM has to be maintained with updates, etc. and becomes just another housekeeping chore.
If Fusion 360 was still available in Linux flavor I would probably have given it a try. Since that is no longer an option I took the lower hassle option of going with OnShape, and so far I have not regretted that decision. At this time, I have been using OnShape for less than a year so I still have much to learn, and I don't think I will be hitting a ceiling any time soon. It took me less than a month to be able to start using the software to do useful things, so it was well worth the time investment.
My conclusion: Pick Fusion 360, OnShape, FreeCAD, or whatever and dive in - you'll learn some useful skills and maybe have some fun doing it.