Connection drops with "Using degraded feature set TCP instead of UDP"

I tried installing r8168 via sudo mhwd --install pci network-r8168 and then echo "blacklist r8169" > /etc/modprobe.d/r8169_blacklist.conf. However after rebooting I don’t get a network connection at all. Am I installing it wrong?

Also, how do I switch the resolver? dnsmasq is apparently already installed, but when I try to start it, it just fails because port 53 is already in use.

sudo systemctl disable systemd-resolved
sudo reboot
sudo systemctl --now enable dnsmasq
Job for dnsmasq.service failed because the control process exited with error code.
See “systemctl status dnsmasq.service” and “journalctl -xeu dnsmasq.service” for details.

I couldn’t figure it out by myself through Google.