I've made a large number of custom prints, and all of them were created using TinkerCad. It's an amazing toolkit, stupid easy to use but versatile. That is ... until something needs a tiny adjustment somewhere. That's when I feel it would've been neat to use parametric CAD instead.
I have spent many hours following Youtube tutorials for Onshape, Fusion, and FreeCAD. Tutorial shapes like a LEGO brick are fairly easy, although I admit that this kind of modeling is a sharp departure from the kid-friendly TinkerCad.
My problem is that I don't want to make simple coasters or keychains, but complex shapes like this one. It's a holder/mount for two different kinds of walkie-talkies that I use, and the blue part slides into a tray in my car's dash where it sits nice and snug.
Question: How the hell do I even get started modeling something like this?? There's not a single straight cuboid here. Everything is slightly wedge-shaped.
The way I do this in TinkerCad is that I build the hollow first: I made a 3d model of the walkie, a little oversized, set it be hollow, and drop it into the shape - that's the red or orange shells you see.
Complex shapes (example: car bumper or PS4 controller) are made in CAD using surfaces. I recommend starting with basic features before moving to surfaces if you decide to go that route. The models from your picture don't look super complex tbh, it could be done by using basic CAD features (drawing cross section(s), extruding, using shell feature, chamfer, maybe some revolve, sweep, loft etc).
I could model these quite easy in Solidworks (a lot of experience), but it would be time consuming in FreeCAD (still learning and trying to force myself to use it instead of SW)
onshape is good too.