In order to set up an Active Directory / Domain Controller on the cloud assigning the IP manually and removing IPv6 prevents any future issue.

Start with a fresh virtual machine and give it a name:

sudo hostnamectl set-hostname ad0

Configure the interface using netplan:

sudo systemctl enable systemd-networkd
sudo rm /etc/systemd/network/05-eth0.network
sudo rm /etc/netplan/00-installer-config.yaml
sudo nano /etc/netplan/00-installer-config.yaml

For the primary AD-DC:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
      dhcp6: no
      addresses:
        - 192.168.133.69/17     # Private IPv4 address.
        - 139.177.192.228/24    # Your Linode's public IPv4 address.
      gateway4: 139.177.192.1   # Primary IPv4 gateway.
      nameservers:
        search: [test.local]    # Search domain.
        addresses: [8.8.8.8]    # DNS Server IP addresses.

For a replication AD-DC:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
      dhcp6: no
      addresses:
        - 192.168.131.39/17            # Private IPv4 address.
        - 139.177.196.132/24           # Your Linode's public IPv4 address.
      gateway4: 139.177.196.1          # Primary IPv4 gateway.
      nameservers:
        search: [test.local]           # Search domain.
        addresses: [192.168.133.69]    # DNS Server IP addresses.

Apply:

sudo netplan apply

On Linode’s dashboard, go to Configurations > Edit > Disable Auto-configure networking > Save Changes for both VMs.¬†Then reboot!

Disable IPv6 on /etc/sysctl.conf, append these lines:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

Apply and reboot:

sudo sysctl -p
sudo reboot

Disable IPv6 also on /etc/default/grub, adding ipv6.disable=1 like shown:

GRUB_CMDLINE_LINUX_DEFAULT="autoinstall ds=nocloud-net;seedfrom=http://10.0.2.2:8309/ net.ifnames=0 ipv6.disable=1"
GRUB_CMDLINE_LINUX="console=ttyS0,19200n8 net.ifnames=0 ipv6.disable=1"

Apply and reboot:

sudo update-grub2
sudo reboot

Check if the DNS servers are configured as needed:

systemd-resolve --status