There are no Qt wrappers for Nim
There is at least QML.
And of course Qt is C++ with MOC, so there are really only very few bindings for other languages available:
https://en.wikipedia.org/wiki/List_of_language_bindings_for_Qt_5
And please note, latest GTK3 is at
http://forum.nim-lang.org/t/2198#15822
I will delete the 3.15 one soon, it is really obsolete.