At the end of 2024 Google changed connection requirements, blocking the old PHP API's one.
Here's what to do to solve:
- Be sure to have installed at least Global Gallery v9.0.9
 - Go in a gallery builder having Google Drive as source
 - In the connections manager box (the one in right sidebar) click on "manage connections"
 - Delete the current one
 - Perform again the connection as explained in the documentation
(NB: while typing this FAQ, Google is still approving the new Global Gallery app configuration, please accept it even it they tolds you it could be unsafe) - Save, select the new connection in the dropdown and click on the "Update connection" button. The connection should be successfully performed
 - Click on the "Update" gallery button