At the right hand side of the Blender UI there is a collection manager that lists all objects, lights, cameras, etc in the scene with their respective collections. Every single object is disabled, how do I re-enable them all at once?
You should make use of collections. Instead of hiding each and every object, just hide/show the entire collection, it’s easier this way. You can also press Alt-H to show hidden objects (or go to Object > Show/Hide > Show Hidden Objects.