Also it looks like this package is available in Ubuntu 20.04 repository:
r8168-dkms - dkms source for the r8168 network driver
You could try download that from a different machine and then installing that it seems that it's the network driver for your LAN card: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
If you get that working first you would then work on getting your wireless card to work. Just thought I'd mentioned it might make things easier.
r8168-dkms - dkms source for the r8168 network driver
You could try download that from a different machine and then installing that it seems that it's the network driver for your LAN card: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
If you get that working first you would then work on getting your wireless card to work. Just thought I'd mentioned it might make things easier.