Not a conventional option, but I've built a few (non-game) GUI applications using Godot game engine + C#. Works great, intuitive once you get the hang of the UI system, fully cross platform (for 3.x anyway - Godot 4 still has a few unsupported platforms - android, web, ios - android support is ready for next release, ios has a PR that I haven't checked up on but I believe it was also nearly ready. Just web that is lagging last I checked.)