My guess is that you need to uninstall the r8168 package, which comes installed by default on EndeavourOS, but is not needed in a vast majority of cases. I could be wrong, of course, but this is worth trying, because it’s so simple.
Run:
sudo pacman -R r8168
Reboot and see whether you get the network connection for those unofficial kernels.
If that doesn’t get you your network connection then you’ll have to install the dkms driver for your specific network card.