UE has a pretty mature cross platform UI framework and Nim happens to have one of the best plugins for UE :-P I really need to do an UI template project at some point.
It has a built in designer, gpu support. ~5 seconds comp times for native Nim. Instant rebuild time for NimScript. Full bindings for both. Plus recently added automatic bindings for native Nim in NimScript (when you compile you can use right away those types in NimScript). Among many more features and more to come :-) If you are curious about it look for UMG (unreal motion graphics). Plus final app is probably way smaller than an electron aberration