The contrib forum module is not visible in admin/modules or admin/reports/updates and therefore cannot be enabled or uninstalled from the admin ui.
Obviously module updates will not be visible in admin/reports/updates
The module can be enabled using drush.
It's not clear whether available module updates can be detected and implemented with composer.
In Drupal 10.x install the module using composer.
View admin/modules and the contrib forum module is not visible. Only the core forum module appears.
View admin/reports/updates and the contrib forum module is not visible.
Enable the module with drush and the same occurs.
The module can only be disabled with drush, and then removed with composer, but only after removing all forum categories.
This may be related in part to https://www.drupal.org/project/forum/issues/3358942 📌 Add a composer.json file Needs review which requests the addition of a composer.json file
Closed: works as designed
1.0
Code
Drupals module discovery system favours a module in /modules over one in /core
So if you have both, the contrib one is in use
I would recommend removing the contrib one from your codebase for now
We wanted to remove it from core for 10.x but didn't complete it. So for now there are no differences, we hope to remove the core one before 11