on Ubuntu / Debian
sudo apt update
sudo apt upgrade -y
sudo apt install python3 python3-pip
python3 -m pip install PyQt5 PyQt5-tools
Location of PyQt5 designer on Windows
C:\Program Files\Python36\Lib\site-packages\pyqt5-tools
or
C:\Users\<User>\AppData\Local\Programs\Python\<version>\Lib\site-packages\pyqt5-tools
on Linux
python3 -m PyQt5.uic.pyuic youruifile -o yourpyfile -x
on Windows
pyuic5 youruifile -o yourpyfile -x
python3 main.py