Automatically disable network activity for apps when on a Portable Hotspot Very often, on my Mac, I'm connected with to the 4g Portable hotspot created on my iPhone.

The mac recognises it as the portable hotspot, and can even turn it on (I understand this came with the latest software latest updates). 

Now I wonder, since it can differentiate between regular Wi-Fi network and portable hotspot created on an iPhone, is it possible to automatically turn off syncing services/apps/ etc. whenever I'm connected to the 4g hotspot?

I'm running macOS Mojave 10.14.2.
Try TripMode. https://www.tripmode.ch

It is an app that blocks unwanted traffic. It remembers settings for different networks, e.g. you can disable it on your home WiFi and enable it on your iPhone Hotspot.

I've been using it for years, should be exactly what you want. A free trial is available.