alt Hacker Newsyeah, op here: it's exactly that. I've used most of the free or open source software options and it seemed like none of them are parametric. I know I could buy fusion or something like that, but I found OpenSCAD before I got to that point and feel like it fits the bill for me.
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FreeCAD is open source and has parametric capabilities. Personally I find it unusably buggy, but apparently there are lots who don't - ymmv.
SolveSpace is open source and has parametric capabilities. It's much more limited in scope (e.g. you can't do filets) but good enough for my purposes.
I've not explored the commercial options beyond TinkerCAD, and that's not parametric. Super easy to bodge something together though :)
Fusion is free for personal use and in my experience at least was much faster experience than OpenSCAD.
You don't necessarily need to buy Fusion, it has a well hidden free tier for personal use, just gotta dig on the site a bit.
I like Onshape. It’s free to use provided that you’re okay with your design being public.
Solvespace and Onshape are free and parametric.
Freecad is fully parametric, set constraints so it’s 0 degrees of freedom and you shouldn’t have that problem.