Qt platform plugin "xcb" not found --- calling run_cheat_debugger() about mametoolkit

I also tried installing Ubuntu 20.04.2 LTS, using the included Python 3.8.10
Qt installed with sudo apt-get install qt5-default After I got the errors, I tried the commonly suggest Ubuntu fix: sudo apt-get install --reinstall libxcb-xinerama0 No change.

Here are the new errors after setting a Qt path variable, and a Qt debugging variable (with just the Qt debugging variable, the results are identical to what I first posted).

pc2@pc:~/Desktop/MAME_Test$ export QT_QPA_PLATFORM_PLUGIN_PATH="/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms"
pc2@pc:~/Desktop/MAME_Test$ export QT_DEBUG_PLUGINS=1

pc2@pc:~/Desktop/MAME_Test$ python3 joust22.py

Debug Build: Disabling input grab for -debug
Debug Build: Disabling input grab for -debug
Debug Build: Disabling input grab for -debug
QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so"
"Plugin verification data mismatch in '/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so'" 
         not a plugin

 **(many repeats of this error for different .so files at this directory location)**  
 **(including libqxcb.so)**

QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/platforms" ...
QFactoryLoader::QFactoryLoader() checking directory path "/home/pc2/.local/lib/python3.8/site-packages/MAMEToolkit/emulator/mame/platforms" ...
This application failed to start because it could not find or load the Qt platform plugin "xcb" 
in "/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms".

Reinstalling the application may fix this problem.
b'\x1b[1;36m[MAME]\x1b[0m> '
pc2@pc:~/Desktop/MAME_Test$ 

Building the modified MAME on your system following the toolkit author's instructions solves this problem.

[sl92983]

I got the same error. Could you share how to fix it? Thanks!