Raspberry PI 4, access to CCTV video stream with android thered internet connection

I am using a raspberry PI4, which would be dedicated to get the stream from CCTV camera, this thanks to OpenCV or other frameworks capable of accesing the RTSP stream.
To access the internet on my Raspberry PI, I am using a thethered USB android phone.

The whole network setup is set as follows:

  1. IP CAMERA Amcrest IP5m-1176EB-28MM, wired (PoE)
  2. Router Linksys WRT54G running OpenWRT – for routing purposes the CCTV camera cannot be connected directly out of my raspberry
  3. PoE Switcth, TP-Link TL-SG1005P
  4. Raspberry PI 4, running Raspbian (uname -a: Linux raspberrypi 5.4.79-v7l+ #1373 SMP Mon Nov 23 13:27:40 GMT 2020 armv7l GNU/Linux) – debian version 10.7
  5. Huawei P20 Lite, with a normal simcard for data plan

I am having the following issues:

  • When I wire up the ethernet cable from my router, wired network (without internet) gets priority and my thetered interent goes down

I tried to:

At the moment I can just keep both (usb thering) and ethernet connected at the same time. I cannot access my RTSP stream.
Should I assign a subnet mask and gateway too, to be sure I can have access to the camera? In the future I am looking forward to add some more cameras.

Thanks in advance,
Euge