The qt-designer.bat file did not launch the QtDesigner. I have tried the file available with OSGeo4W64 installation but the qt-designer did not starts.I also try to start the qtdesigner from the QtDesginer with QGIS 3.10 custom widgets but also did not start. I have tried this solution in this link: No custom widgets in Qt Designer for QGIS 3
Note Qgis is v3.4