In the MVP of federated properties, only remote properties can be used when federation is enabled. Local properties are not supported and will cause issues [See T255404].
To prevent Wikibase editors from creating local properties and unintentionally breaking their instance, we should prevent access to Special:NewProperty.
BDD (Scenario: viewing SpecialPages)
Given My Wikibase has federated properties enabled
When I load the page Special:SpecialPages
Then Special:New Property is not displayed in the list of Wikibase special pages
BDD (Scenario: directly navigating to NewProperty)
Given My Wikibase has federated properties enabled
When I try to access wiki/Special:NewProperty
Then the standard message is displayed stating "You have requested an invalid special page."