PyQt6 is a Python binding of the cross-platform GUI toolkit Qt. Applications built with PyQt6 will run on any platform supported by Qt & Python including Windows, OS X, Linux, iOS and Android.
Created by Riverbank Computing, PyQt is free software (GPL licensed) and has been in development since 1999. The latest version PyQt6 was released in 2021 and the library continues to be updated.
For a complete guide to desktop application development with Python & PyQt6, see the PyQt6 tutorial and PyQt6 book Create Simple GUI Applications with Python & Qt.