Pretty much all the material they've pushed for, uhm, almost 15 years...?
Widgets are still supported (because they work, and they are used by lots of faithful Qt customers), but QML is where they've put pretty much all their development focus since the late 2000s.
I think the point is "by whom" ? Does Qt say that somewhere? I haven't seen it. They certainly push QML, but they certainly are still activatly maintaining and improving their "old fashioned" widgets as well.
Not sure there is anything official, but I just uncovered this sentiment in my research after scouring tons of chat forums, etc. while researching GUI toolkits. There seems to be an understanding that QtWidgets is in "maintenance mode" and I'm told hasn't seen any new features in a while. I've also noticed many existing projects discussing migrating to QML (many don't, however, due to the amount of work).
Widgets are still supported (because they work, and they are used by lots of faithful Qt customers), but QML is where they've put pretty much all their development focus since the late 2000s.