Hi @jakejake
The official n8n docs states that the Notion node only supports displaying the data relation property for two-way relations. When you connect two Notion databases with a two-way relationship, you can select or filter by the relation property when working with the Notion node’s Database Page resource.
There are multiple threads on the community forum where users are complaining that relation properties don’t appear. Have a look at these previous post.
Hope this helps