The APN or "Access Point Name" determines how the data connection is processed in the network, mobile devices usually have a configuration field for the APN somewhere in the settings menu.

I have never personally used a MAC, so I can't tell how this setting is made in macOS. In Windows it is now a system wide setting but before that it was a setting you made in an app that came with the USB stick. I suppose it may be either of those options on the Mac as well.

Can you tell the excact type of USB stick you are using, maybe I can pull the manual and look for the APN setting. Does the USB stick use a companion app from Alcatel or is it controlled purely with macOS onboard utilities?

If you have an iPhone or Android device with a second  SIM slot (many newer models have them) you might as well do away with the USB modem and put the data SIM into the phone. You can then open a mobile hotspot on the phone to which the laptop can connect via Wifi. Maybe you can work around the streaming problem this way.

Using the phone has other advantages over the USB modem too: Phones usually have much faster LTE or 5G modems, compared to the stick, plus you can place the phone where the signal is good (e.g. near a window)  and still use the laptop wherever it is convenient.

Thanks a lot for your help, I actually did put the sim in my phone to use it as a hotspot which seemed to work. I'd just prefer to be able to do it on stick since I only have one simslot. 

To answer your questions: the device I'm using is an "Alcatel One Touch IK40V LTE Stick" which doesn't seem to need an app although it does say so in the manual (once you plug in the stick the software is supposed to install, but this didn't happen so I just set it up via network sharing settings).

An in the network sharing settings there is no menu for an APN or "access point name" or "zugangspunkt" if it is a German language system?