It appears a recent update broke pitivi. While I am not great at reading python errors, I believe that the error is caused by a library incompatibility.
Gdk-Message: 08:44:27.571: Unable to load tcross from the cursor theme
Traceback (most recent call last):
File "/usr/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3.py", line 43, in <module>
cursors.SELECT_REGION: Gdk.Cursor.new(Gdk.CursorType.TCROSS),
TypeError: constructor returned NULL
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/usr/bin/pitivi", line 166, in <module>
_run_pitivi()
File "/usr/bin/pitivi", line 143, in _run_pitivi
from pitivi import application
File "/usr/lib/pitivi/python/pitivi/application.py", line 32, in <module>
from pitivi.mainwindow import MainWindow
File "/usr/lib/pitivi/python/pitivi/mainwindow.py", line 29, in <module>
from pitivi.editorperspective import EditorPerspective
File "/usr/lib/pitivi/python/pitivi/editorperspective.py", line 41, in <module>
from pitivi.timeline.timeline import TimelineContainer
File "/usr/lib/pitivi/python/pitivi/timeline/timeline.py", line 35, in <module>
from pitivi.timeline.elements import Clip
File "/usr/lib/pitivi/python/pitivi/timeline/elements.py", line 29, in <module>
from matplotlib.backends.backend_gtk3cairo import FigureCanvasGTK3Cairo as FigureCanvas
File "/usr/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3cairo.py", line 6, in <module>
from . import backend_cairo, backend_gtk3
File "/usr/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3.py", line 49, in <module>
raise ImportError(exc) from exc
ImportError: constructor returned NULL