Description of problem:

Probably since the Mageia 7 mass rebuild, Meld does not start anymore.

The error on console is showing (same when started as root):

quote
$ Traceback (most recent call last):
  File "/usr/bin/meld", line 358, in <module>
    import meld.meldapp
  File "/usr/lib/python3.6/site-packages/meld/meldapp.py", line 29, in <module>
    import meld.ui.util
  File "/usr/lib/python3.6/site-packages/meld/ui/util.py", line 20, in <module>
    from meld.ui import gladesupport  # noqa: F401
  File "/usr/lib/python3.6/site-packages/meld/ui/gladesupport.py", line 10, in <module>
    from meld import sourceview  # noqa: F401
  File "/usr/lib/python3.6/site-packages/meld/sourceview.py", line 93, in <module>
    class MeldSourceView(GtkSource.View):
  File "/usr/lib64/python3.6/site-packages/gi/module.py", line 215, in __getattr__
    wrapper = metaclass(name, bases, dict_)
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

[1]+  Exit 1                  meld
unquote