> I'd like to mess with Qt but the GUI builder is with their paid licensing iirc i think, but it seems to be the only cross-platform solution afaik
{apt, brew cask, choco} install qtcreator
it's entirely free & open-source. there is Qt Designer Studio which adds a couple of convenience functionalities if you are making e.g. embedded appliance dashboards but for 100% of desktop UIs you have everything needed in the LGPL qtcreator