Is this for creating designs to fabricate with a laser? Or something else? Are you mainly interested in the renderings or, in some other specific output?
FreeCAD hasn’t been mentioned. It does the core things Fusion 360 does. It is community-developed (like Inkscape) while Fusion 360 is commercial. Concepts (planes, sketches, constraints, parametric parameters, etc.) transfer pretty well between the two. I recently discovered that there is even a FreeCAD box generator.
In addition to the usual tutorial stuff on YT, HackSpace magazine has a FreeCAD book: FreeCAD For Makers
I Like to Make Stuff has a Fusion 360 for beginners course that is rumored to be excellent.
I use Nomad Sculpt on the iPad for modeling more organic stuff (mostly for 3D printing but, I have made some 3D carvings on the Glowforge).
Blender is more complicated but, mostly does it all. If I want a pretty rendering, Blender is hard to beat for quality and control. Learning Blender is a lot to bite off for just making box-like things, though.