While you cannot activate the DLC code/keys ingame, you can still activate it via Ubisoft Connect/Uplay. This should give you the extra skins (Altaïr's robes, Armor of Brutus and Turkish Assassin armor). I can't confirm if this would give access to Vlad the Impaler's Prison as I haven't reached that part yet.

The Lost Archive unfortunately cannot be accessed. You can see it in the main menu but selecting it does nothing.

UPDATE: Activating this in Ubisoft Connect/Uplay will give you access to Vlad the Impaler's Prison

While you cannot activate the DLC code/keys ingame, you can still activate it via Ubisoft Connect/Uplay. This should give you the extra skins (Altaïr's robes, Armor of Brutus and Turkish Assassin armor). I can't confirm if this would give access to Vlad the Impaler's Prison as I haven't reached that part yet. The Lost Archive unfortunately cannot be accessed. You can see it in the main menu but selecting it does nothing. UPDATE: Activating this in Ubisoft Connect/Uplay will give you access to Vlad the Impaler's Prison