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