Install Qt Designer Standalone for pyqt5 python

Via command line

pip install pyqt5-tools

then run it

pyqt5-tools designer

usually its on for pyqt5-tools :

C:\python310\Scripts\pyqt5-tools.exe

and designer on this

C:\PYTHON_INSTALATION\Lib\site-packages\pyqt5_tools\Qt\bin

or

C:\PYTHON_INSTALATION\Lib\site-packages\qt5_applications\Qt\bin