Over the past few years, I've built a fair few UI's using QML (Qt's DSL for writing UI code) - proper ones, including one for a mission-critical / safety-of-life application, and another powering the tool to be used across a large group of non CS types. In other words, things that had to work, and not just be interactive "nice to have" toys (aka research prototypes).
Memorably, I was once asked during an interview whether I would recommend using QML and/or how it compares to using the more battle-tested QWidgets. At the time, I'd only really used it for a bunch of research prototypes (i.e. implementing HCI experiments to be exact), where it presented a great environment for implementing the kinds of dynamic non-traditional interfaces I needed. For that it was great and saved a lot of time. But, admittedly, it did also throw up a bunch of glitches (e.g. randomly sampling garbage from the wrong texture buffers / other applications even, particles not showing when chaining several scenes together but being fine when used in isolation, etc.). At the time, I could only attribute some of these to me perhaps trying to combine a few too many highly experimental techniques where perhaps the framework hadn't been tested so great.
However, knowing what I do now, I would strongly recommend that unless you were building something non-mission critical, and where the thing is loaded with animations / dynamic effects, that you really shouldn't be using it. Sure, you may be able to knock out a prototype quite quickly - but at some point - often at ill-timed moments, you will randomly stumble across one or more intractable bugs / quirks from left field that have you scrambling to rewrite / refactor the whole lot.
Disclaimer: Just to be clear - I generally do still like the idea of the QML language, and I think it does many things right. However, there are also many ways in which the "declarative paradigm" is really awkward to work with (*ahem* creating dialogs / temporary items / sequential-flow-based-types / etc.)
More disconcertingly though, implementation-wise, it is seriously lacking in quality / completeness / stability, etc. in enough ways that mean that I cannot in good conscience recommend any new greenfield projects to start adopting it now.