I don't remember when ctrl G created a collection visible in View Layer or Scene views in 2.8.

Since months, now, you have to press M, instead, to avoid to go to Blender File view to link collection to scene through right click menu.
I thought it was clear. M to see collection into View Layer organization. Ctrl G to avoid collection appearing into View Layer organization.

But I agree that is a little bit weird to be able to use a collection in Scene as a group in scene properties that does not have status of a collection linked to scene.

Maybe that is not great to link colections as fake users. But currently, outliner is missing tags and filters for collections to avoid to display those that are not pertinent according workflow step.

hi, @ronan ducluzeau (zeauro) the main issue here is the Ctrl G adds superfluous data to your blend file. There's no way for the user to know what's going on here unless they are familiar with the Orphaned data section. I used the Ctrl G simply testing hotkeys, it took some time to find where the collections were created. I ended up with many fake user collections and they were saved with the .blend file not purged on file save reload. Maybe this is not technically a bug but it's certainly not good practice to allow users to create persistent hidden elements in their .blend files. If this was not ready for release, it should have been disabled.