The function https://doc.qt.io/qt-5/qquaternion.html#fromEulerAngles preassumes a very specific order of Euler angles and rotation sequence. There are several conventions, and it is usual in geometry packages to allow the user to specify the rotation order as an argument. Something like:

yaw = 0.1; 
pitch = 0.2; 
roll = 0.3;
quaternion = fromEulerAngles( yaw, pitch, roll, "ZXY" )

Potentially, this Qt function could be expanded to allow this rotation order as fourth argument. A very good example on how to implement this could be found here:

https://github.com/bminortx/Buckshot/blob/master/matlabComponents/Matlab_functions/angle2quat.m

 https://www.mathworks.com/help/aerotbx/ug/angle2quat.html