The errors in your screenshot above, and this one in the French forum, both involve non-standard blocks: block_manager_resultsoverview and block_formation. These aren't part of core Moodle, nor are they available from the Plugins directory. Maybe the former employee wrote these, or maybe they came from some third party. Either way it looks like these plugins may be causing the errors, but since we don't have the source code we cannot provide much help.
Possibly if you shared the plugins' source code (for example, by attaching a zip file of the blocks/manager_resultsoverview and blocks/formation subfolders) we may be able to help further. But 1) you may need the permission of the copyright holder to publicly share this source code, and 2) unless the plugins are fairly trivial you may need for more advanced support that the community can provide.
Of course, I could be wrong and the above plugins are not the cause but instead are being affected by the errors.
Except that for sorting reasons in the general course catalog (sorting by ID), I realized that this new course, with this old ID, couldn't go up.
This may be a translation issue, but I think the course catalog is specific to Moodle Workplace which is only available with commercial support. Maybe you mean course category?
