Can't connect to wired ethernet on Ubuntu 20
If you can reach an internet connection via wifi or USB tethering a mobile device that supports it, try to install r8168-dkms. This should be a temporary solution until r8169 that's provided in the kernel works properly on your device.
Try to run sudo apt install r8168-dkms and reboot. I have the same ethernet controller as you and this solves my problem most of the time. Mine works out of the box in 21.10 so the issue you're having is fixed in later versions of Ubuntu.