open iOS-app in MacOS-dock

My wife owns a MacBook Pro 13' and a iPhone SE, if she is working on her MBP and simultaneous opens an app on her iPhone, the use app also appears left in her Dock on MacOS as an icon.

I think this is a cool feature (although not really use-full) but on my MBP dock nothing appears when I start an app on my iPhone. I guess this feature uses bluetooth? Bluetooth is switched-on on both devices. They are also on the same wifi-network.

How can I enable this feature?

MacOS Mojave 10.14.6, iOS 12.4.1