Open /etc/NetworkManager/NetworkManager.conf and add:
[main]
dns=none
sudo systemctl restart NetworkManager.service
Add any server that you want to /etc/resolv.conf. For example, I use 127.0.0.1 because I have installed dnscrypt-proxy.
nameserver 127.0.0.1
# /etc/resolv.conf.head
nameserver custom.dns.ip.addr