Hi @DemouserDemouser, instead of right-clicking a layer in a Map in ArcGIS Pro, you could try opening a brand new ArcGIS Pro Project and use the Catalog pane to connect to the geodatabase as the database user who owns the dataset (if you are using an Enterprise Geodatabase), right-click the feature class Data Design => Attribute Rules. This might make a difference? If you are using a File Geodatabase, try using the same method, but obviously there is no need to connect as a particular database user.
It looks like the Feature On Feature Ready to Use Rule is designed to check for a spatial relationship between a given feature class and another feature classes. Make sure that any other feature classes you want to specify as the Features To Compare are accessible using the same geodatabase connection.