I use wx for my own stuff and also use a lot of wx-based applications. Wx is quirky and has some bugs but it's not going to go away or have a massive breaking change without warning. Its biggest weakness is the slow release schedule which leaves users waiting for a long time to access things that are critical on changing platforms (macos is a massive pain to support as the underlying system changes all the damn time). My opinion of it can be summarized as "the worst, except for all the others" so I keep using it.
I keep considering Qt whenever I start a new project and I'm still scared to use it. It's controlled by a company that is in really bad shape financially and has a history of attempting stupid things for short-term profit and screwing over customers. It's reasonable if you can manage with either just the LGPL components or if your entire project is GPL, but if not their license terms are really terrible and get worse and worse over time. They keep making changes that fuck over their paying customers. I don't feel good about using this at the moment. The KDE people have thankfully got that company by the balls with a watertight contract, and I totally trust the KDE people, but there's still plenty of damage the company can do, and every sign they will. It's really unfortunate because Qt is otherwise an excellent platform.
Multiplatform gtk is a pain. There are a few projects that successfully pull it off (Horizon EDA is a notable example) but I don't think I could manage it myself.
If you're doing a new thing you might want to consider one of the many imgui implementations (as you seem to be thinking in that direction already).