After disabling everything, plugins, themes, re-installing WordPress, there was still an PHP notice being dump in the Media Library screen
Trying to get property of non-object on /wordpress/wp-includes/capabilities.php
Well, it’s a documented bug and even has a cute GIF:
The ticket refers to Comments of a non-existant Custom Post Type. If the CPT is deactivated, Comments attached to it will dump the notice. I experienced the same with attachments. Activating the CPT back “solves” the issue.