When my regular ISP has issues, I use my LTE phone as backup. This allows me to replace my Internet modem with my phone using a USB-C to Ethernet adapter.
I do this by using a Dell USB-C to Ethernet adapter which I connect the phone's data/charging port. Then I turn on the Hotspot Ethernet sharing (under the connections settings).
The phone in the video is a Samsung FE20.
I made a similar video about this topic which you can find here:
• Connect phone to Home Router