Python GI repository: cannot import name Flatpak, introspection typelib not found

Question

I'm writing GTK4 application in Python. I'm trying to import Flatpak from PyGObject

from gi.repository import Flatpak

However, when I run my app I got this stacktrace:

Traceback (most recent call last):
  File "/app/bin/package-transporter", line 48, in <module>
    from package_transporter import main
  [...]
  File "/app/share/package-transporter/package_transporter/installer.py", line 1, in <module>
    from gi.repository import Flatpak
  File "/usr/lib/python3.10/site-packages/gi/importer.py", line 136, in load_module
    raise ImportError('cannot import name %s, '
ImportError: cannot import name Flatpak, introspection typelib not found

What did I do wrong ?