@francogpellegrini, @fernando-sismonda, I just tested with netplan yaml similar to yours, and i can't reproduce any problem; the dhcp dns server is correctly ignored on my test system. What versions of netplan, and systemd, do you have installed? Also, what's the content of your /run/systemd/network/* and/or /etc/systemd/networkd/* files?
@francogpellegrini, @fernando-sismonda, I just tested with netplan yaml similar to yours, and i can't reproduce any problem; the dhcp dns server is correctly ignored on my test system. What versions of netplan, and systemd, do you have installed? Also, what's the content of your /run/systemd/ network/ * and/or /etc/systemd/ networkd/ * files?