Might I ask, why exactly do you feel the need to have a webapp for CAD rather than a hard client?
Freecad in a VM with a remote viewer like guacamole?
Ideally you could use moonlight but that is not web based
What about solvespace web build: https://github.com/solvespace/solvespace/tree/emscripten#building-for-web
Would love to learn if it exists too. I use it often.
The only other way I know how to CAD is https://github.com/pythonscad/pythonscad
Unrelated but BTW FreeCAD is fully python scriptable. In fact, as I understand it, every operation is first translated to python code.
There is also Cascade Studio (Demo). Sadly development has stalled, it was a really cool project.
Probably not at all what OP is looking for though since TinkerCAD is just sketch/primitive type workflow, not like openscad.
Someone posted this https://webvm.io/alpine.html in another community and it made me think of this post. I’ve never used webvm and I suspect there are many downsides but seemed relevant and the demo seems to be able to run a full desktop environment. You have to find a CAD software that supports Linux though which is a controversial topic at best.
Check out Kasm too, you can easily install blender into it.