I was able to build things with Qt and Qt3D I wasn't sure would even be possible before starting (a very narrow-scoped robotics automation planner/simulator). It was remarkably easy to get moving with.

Ironically the first version was mocked in Unity, thinking the tooling and ecosystem would make the MVP easy to build. It wasn't terrible, but it wasn't particularly easy either. The end result was extremely heavyweight and gave terrible performance. Qt on the other hand yielded fairly snappy and lightweight results, and the development experience wasn't bad at all.

I wonder why more people don't use it, but then, that's my only exposure. Maybe it's not so great for other things, and I suppose there's the whole matter of having to pay for certain tooling and support. Us developers are sometimes super-hesitant to pay for the tools we use, haha.