Trolltech was skimpier but was much more interested in the success of the platform per-se. In many ways the post-Nokia experiences are an attempt at re-discovering the space Trolltech lived into.
> their open source OS based on Qt.
There was never such a thing. They had a Symbian OS skinned with Qt, and a number of Linux incarnations that started with GTK and were later reskinned with Qt. It didn't help that they stroke a high-level agreement to basically adopt Intel's Linux efforts, which were targeting GTK. By the end of these travails, they ended up with something fairly decent but that was just a lame-duck. Nothing was ever "based on Qt" at a fundamental level.
https://en.wikipedia.org/wiki/MeeGo which evolved to http://merproject.org/ and https://sailfishos.org/ after the Nokia era