All the important parts of Qt are available under LGPLv3. This only makes a difference to you if you want to do Tivoization of your software (Gtk uses LGPLv2, this being the only major difference AFAIK). In which case you still have the option to buy a commercial license.
Yeeeeahhh.... at the moment. They have gotten really aggressive about commercial licensing recently, and even a conservative extrapolation should give one pause.
Today they might limit themselves to forced registration, SEO, and spamming business contacts with carefully crafted statements designed to stir fear, uncertainty, and doubt around free licenses by strongly suggesting (without actually claiming) that commercial use without a commercial license is illegal. But tomorrow? Also, keep in mind that a business partner who isn't already familiar with Qt and LGPL is going to be about 10x more susceptible to the FUD. That's the whole idea.
My guess: 30% chance of an ugly fork and lots of drama in the next few years. Then, absent a change in direction, another 30% chance in the few years after that, and so on.
Yes, there is a lot of FUD about the licensing for Qt when you search online, definitely not helped by how unclear the Qt site's explanation of it is (to me at least)
My boss looks at this page, he sees that open source programs can use Qt for free and that commercial programs need to pay. That's not the case, but the page is carefully worded to prevent him from confidently coming to the correct conclusion.
If this were the extent of the shenanigans, I wouldn't be mad. I like having a "help me sell this to my boss" page. But it isn't the extent of the shenanigans. They went around me to shake someone down on my behalf (as I perceive it). Last time it was my boss. Next time I choose a GUI framework for an open source side project, I'll primarily worry about it being my users.
Qt being C++ also makes creating language bindings often harder so not all languages will let you build a Qt interface. GTK is C so it's more straightforward.
Both reasons are why I'm trying to develop an OSS alternative with easiness & platform-independence of the web but much lower system requirements than what electron has.
This is ultimately why I went with gtk in a recent Rust project. Qt bindings are a pain, and the license stuff was coming out. But most of the native Rust GUI libraries don't even try. Maybe its a maturity thing and they'll get there but I picked GTK for now
Note though that GTK has no accessibility support on Windows and Mac. If you're only targeting GNOME, then that's fine. For something that's more or less accessible cross-platform, I'd go with wxWidgets or something Web-based.