i have a problem with PyQt5 Designer. I install PyQt with -pip install PyQt5 and then -pip install PyQt5-tools
everything OK. But when i try to run Designer it open messagebox with error: This application failed to start because no Qt platform plugin could be initialized!
how to deal with it?
Go to => 
Python38>lib>site-packages>PyQt5>Qt>plugins
In plugins copy platform folder
After that go to
Python38>lib>site-packages>PyQt5_tools>Qt>bin
paste folder here .  Do copy and replace.

This will surely work..
Now you can use designer tool go and do some fun with python...
PyQt5 Designer is not working: This application failed to start because no Qt platform plugin could be initialized