In SharePoint list columns there is a property named validation of type columnValidation but this property is not returned in a get request. Could this property be added please.
The get request query I am using in Graph Explorer is in the format https://graph.microsoft.com/v1.0/sites/{site-id}/lists/{list-id}/columns which returns the column properties, apart from validation.
The list of properties available can be seen here: https://docs.microsoft.com/en-us/graph/api/resources/columndefinition?view=graph-rest-1.0