On this page, you will find out if Diablo Immortal has Cow Level.
The Cow Level is a secret location that you have to reach by using a portal. After moving to this land, the players are attacked by groups of cows armed with battle-axe.
At the time of writing this guide, there is no confirmed information that Diablo Immortal has a Cow Level, so at the moment it must be assumed that it simply does not exist. It is possible that such a level will be added to Diablo Immortal with one of the updates, but you will have to wait for confirmation.