"all it takes to draw a widget on the screen" is not enough to create "an actual desktop toolkit".

If you need to draw a widget on the screen, there's Dear ImGui [1] that you can use from Go [2]

If you're looking for a desktop toolkit, there's a reason why things like Qt are multidecade endeavours.

[1] https://github.com/ocornut/imgui

[2] https://github.com/inkyblackness/imgui-go