This was confirmed by Sony themselves in the Sony Mobile forums where a Sony Xperia rep said, “The my Xperia service and Protection by my Xperia are discontinued starting from Xperia XZ Premium, that is why you can’t find the service in the settings menu of your device. You can instead use the Google app/service called ‘Find My Device’ to for example, remotely lock and/or wipe your device.”
As Sony points out, users will now be able to use Google’s own service if they’d like the same features. As Xperia Blog notes, the similarities in both services are almost identical, which means that it’s more about users having to switch apps as opposed to having to learn a completely new app/service. It does seem a bit sad that Sony is shuttering their own services, which we guess is in line with the company’s efforts at reducing their focus on certain markets, so by using their resources wisely, they’ll be able to concentrate on other areas instead.