If someone paid me to do something similar, I would probably be building on top of this: https://github.com/Const-me/Vrmac

There’re two hard problems there.

One is how to render vector graphics and fonts. So far, only web browsers do that in a cross-platform way. Windows has it’s Direct2D and DirectWrite, while Linux has nothing comparable, unfortunately.

Another higher level one is how to build easy to use GUI library on top of that. Have not approached that one. I have a few ideas but did nothing so far to address them, lately I’m too busy with other projects.