Description of problem:
Trying to run Frescobaldi for the 1st time since my upgrade to Mga8, and discovered this program can't start anymore.


This is what I get if I run it through a terminal:
$ frescobaldi 
Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/plugin.py", line 79, in instance
    return _instances[cls][obj]
  File "/usr/lib64/python3.8/weakref.py", line 383, in __getitem__
    return self.data[ref(key)]
KeyError: <weakref at 0x7fea0a146270; to 'type' at 0x111c9b0 (PanelManager)>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/frescobaldi", line 28, in <module>
    main.main()                     # Parse command line, create windows etc
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/main.py", line 210, in main
    win = mainwindow.MainWindow()
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/mainwindow.py", line 129, in __init__
    self.createMenus()
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/mainwindow.py", line 1105, in createMenus
    menu.createMenus(self)
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/menu.py", line 61, in createMenus
    m.addMenu(menu_file(mainwindow))
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/menu.py", line 95, in menu_file
    m.addMenu(snippet.menu.TemplateMenu(mainwindow))
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/snippet/menu.py", line 146, in __init__
    self.addAction(self.tool().actionCollection.templates_manage)
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/snippet/menu.py", line 58, in tool
    return panelmanager.manager(self.mainwindow()).snippettool
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/panelmanager.py", line 38, in manager
    return PanelManager.instance(mainwindow)
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/plugin.py", line 84, in instance
    result.__init__(obj)
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/panelmanager.py", line 70, in __init__
    self.loadPanel("musicview.MusicViewPanel", "viewers")
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/panelmanager.py", line 107, in loadPanel
    __import__(module_name)
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/musicview/__init__.py", line 59, in <module>
    from . import documents
  File "/usr/lib/python3.8/site-packages/frescobaldi_app/musicview/documents.py", line 29, in <module>
    import popplerqt5
RuntimeError: popplerqt5 cannot import type '����' from PyQt5.QtCore


The system is an up-to-date Mageia8 with:
$ rpm -qa | grep frescobaldi
frescobaldi-3.1.3-1.mga8
$ rpm -qa | grep lilypond
lilypond-doc-2.20.0-4.mga8
lilypond-2.20.0-4.mga8
$ rpm -qa | grep python3-qt5-core
python3-qt5-core-5.15.2-2.mga8

Not sure if this is related to bug #19757 but python-qt5-webengine is NOT installed on my system, and frescobaldi used to start without it on Mga7.