As it happens Qt has very generous licencing terms. Even for commercial use.
What I meant was I just don't look/use software that needs to be licensed.
I don't do commercial work any more.
The only one I use is licensed Altium, but none of my PCBs are commercial.
Altium also has a ridiculous learning curve, but I have used it since the DOS era.
This might change in retirement when I might need to make some income.
Still have a few years to find/master the open source versions with their many license variations.
Commercial use, that probably should be a deciding factor in choice of tools.
Commercial products are served well by commercial software like QT.
Commerical Compilers/RTOS like Wind River, Vxworks have been around for along time.
But for hobby use, one off, non commercial, hack something together quickly?
End use determines what toolset?
Pis in commercial/industrial applications verses a hobby project.
The OP has not said what project.
How long to learn use the toolset., how long has been allocated for the project.
My few attempts to use QT over the years never impressed me with it's speed of learning.
FreeCAD is quick to learn but Solidworks is Commercial and much harder to learn at the start.
Time, Quantity, Quality. - QT does the two Q's but until you learn it Time will flow away.
Kivy being Python based is a bit quicker, but is newer and how well does it work on small LCDs?
Also not sure if the Kivy Pi4/Python/VC6 issues are fixed yet.
None of this helps the OP. as details of the project are missing.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges