On python version 3.8.10  works fine and you can run PySide6  application 

on python version 3.12.5 we encounter this issue

qt.qpa.plugin: From 6.5.0, xcb-cursor0 or libxcb-cursor0 is needed to load the Qt xcb platform plugin.
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: vnc, xcb, offscreen, vkkhrdisplay, wayland, eglfs, wayland-egl, linuxfb, minimal, minimalegl.

Solution:

Install the libxcb-cursor0 on Linux ** 

sudo apt-get install libxcb-cursor0
 
Package Info: https://packages.debian.org/sid/libxcb-cursor0

The pyside6 package  dependency in the pyproject.toml 

pyside6= ">=6.6.1"