I'm afraid you vastly underestimate what it takes to produce a competent GUI toolkit. Performance, portability, layout control, theming, keyboard control support, accessibility for things like screen readers, and, of course, a sane API.
And I don't mean the code, I mean the design / architecture / UX expertise.
In what sense am I underestimating it?
> Yes, it will be a grind to get anything working without those
Those being the GUI toolkits like Qt and KDE one.
But yes, I agree, I have done UIs in low level (Skia) and high level (web, android) and I know it is a lottttt of work.