Can not add library

[taku-s]

Hi all

I am trying to make a desktop GUI app on Windows 10 using Python 3.8+Visual Studio 2019.
I have installed PySide2 on Python3.
I launched QtCreator 4.13, placed the labels and buttons in design mode and saved the form.
But when I open the project again I get the following error

It looks like Qt Creator closed because of a problem with the "QmlDesigner" plugin.
Temporarily disable the plugin.

Qt Version is Qt 5.12
Kit is Desktop Qt 5.15.0 MSVC2019 64bit
Imported library is QtQuickCpntrols 2.15