

Are you looking to build a keyboard from a kit, or design one from scratch?
SplitKB.com has forked a few popular open source keyboard designs like the Corne or the Sofle. Even if you don’t end up purchasing their kits, they have some excellent build guides and documentation. If you’re a keyboard or DIY electronics beginner, it’s a good way of seeing what sort of techniques and tools you’d be in for when soldering things like microcontrollers, switches, and diodes. https://docs.splitkb.com/product-guides/aurora-series/build-guide
If you’re interested in designing a keyboard, I’d recommend looking into the keyboard layout editor Egogen. https://github.com/ergogen/ergogen
Just mashing together shape primitives and Thingiverse parts in TinkerCAD is entirely underrated. It’s still primarily what I use unless I need particularly curvy corner.
Fusion360 and FreeCAD are the CAD versions of Photoshop and GIMP (if Photoshop had a restricted free tier). They’re both trying to be a legit piece of CAD software, so there’s a bit of a learning curve coming from TinkerCAD. I found it easier to “feel my way around” Fusion360’s UI. FreeCAD has a layer of, “How did Open Source devs decide to be different here?” on top of learning something new.