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Qt is about the last library I'd call modern in terms of C++ dialect it employs or requires...

(There are worse but deprecated like MFC. Or on par like wxWidgets.)

I suspect your intel on Qt's C++ use is a bit out of date. Qt nowadays uses (and requires) C++11, as well as more modern constructs.

Qt may be inspired by modern C++, but you don't get hands on experience using the STL since Qt re-implements almost the entire thing.