Honestly the only one I have used successfully and the one I see most professional companies choose is Qt. Yes you possible have to pay for a license when you

Honestly the only one I have used successfully and the one I see most professional companies choose is Qt. Yes you possible have to pay for a license when you get to that point, but they work with small companies/startups and the license fees are not crazy and it saves you tons of time while making your app performant, portable and clean. Gtk to me is just not worth the effort, it is a mess and documentation is horrid. We tried Gtk on one project I worked on a while back and it was abandoned because of the struggles we had to go through just to make it work as expected. While Qt isn't a panacea by any means, it is lightyears better than Gtk. I know I am pissing off someone that knows Gtk well and can't see why it is hard to use, but coming from the perspective of I need to get an app running and not struggle through a framework, Gtk just doesn't cut it. And especially if you are talking about graphing, performance etc, Qt will be the best of them. While you are on the open source Qt you get community support and lots of help/examples. And if you do reach the point you are paying for a license then at least with Qt you will get quick support and problem resolution not based on a communities best efforts which may not align with your companies issues. If I didn't mind some pain in framework maturity, I'd probably try Flutter. Flutter desktop is in early previews IIRC, but it (at least for mobile) is documented much better and is easier to use than Gtk IMO. Flutter does work pretty well for mobile, but that's the only thing I've used it for, so no clue on what the desktop preview even looks like.