Cannot select a foreign item when collection has a M2O to a singleton

[jaads]

Checklist

• I'm using the latest version of Directus
• There's no other issue that already describes the problem.
• I've completed all Troubleshooting Steps.

Describe the Bug

When a collection referes to another collection with an MSO relationship, and the related collection is a singleton, the drawer of the M2O interface doesn't show the singleton item - the drawer is just blank.

Screen.Recording.2023-03-07.at.08.33.01.mov

To Reproduce

1. Create a collection as and mark it as singleton
2. Create another collection with a M2O relationship to the singleton collection
3. Open the collection with the related singleton collection and click on the m2o interface.

The drawer will open but will not contain an item.
When the collection from step 1 is not a singleton, the behavior is as expected so the items will appear in the drawer and one can be selected. But when the collection is a singleton, no item is shown.

Hosting Strategy

Self-Hosted (Custom)

[jaads]

/linear

[github-actions]

🤖 Linear issue created! Maintainers can access it here: ENG-789

[Nitwel]

I'm wondering what the right approach to solve this would be. We could fix the bug to support singletons in relations, but then you could end up with multiple singleton items in the database even though the app can only ever show one, which is not good at all. We could also do as the m2a is currently doing it by disallowing to select singletons on the relation which makes sense to me.