Hi @trantrongtri7993 welcome to the forum!
Your understanding of sounds correct (although GPL is also open source, just comes with additional obligations).
The first reason for using PyQt5 was that it existed! The initial release was in (2016) before PySide2 (2018) – and the early releases of PySide2 were quite buggy. The upshot of that was that more people used PyQt5 and that built momentum in its favour.
While the GPL adds additional obligations, for many use cases that isn’t actually a problem. I started using PyQt5 it for academic research software for example, and open source licenses are standard there. In commercial software many companies are happy to pay the license fee in exchange for support + the ability to use their own proprietary license (vs. the LGPL).
I use both but probably still default to PyQt5 – I prefer the way it handles
.ui files. The good news is that it really doesn’t matter. I’d recommend trying both and converting something from one to the other, just to see how easy it is!