Left of field, but game engines have figured out translating a single set of UI APIs to multiple graphics backends already.

Alternatively you could use a compatibility version of OpenGL, like 3.3 which will run on any desktop OS, then use a windowing lib like glfw and UI framework like Dear ImGui which is graphics API agnostic. I use this particular combination all the time and it never lets me down. Sokol is another options which is a very thin layer over many graphics APIs.