This is a set of steps that will create a custom image of Ubuntu
Server which can then be deployed to a Raspberry Pi 4 without a
monitor.  Please be sure you understand each command before
running it.

firefox https://ubuntu.com/download/raspberry-pi

xzcat ubu*.img.xz > custom.img & progress -mp$!
mkdir -p /mnt/rpi; losetup -f custom.img; losetup | grep custom.img
partprobe /dev/loop???
mount /dev/loop???p2 /mnt/rpi; mount /dev/loop???p1 /mnt/rpi/boot
sudo -i; cd /mnt/rpi; mkdir root/.ssh; chmod 777 root/.ssh
cp -p  /root/.ssh/{authorized_keys,config,known_hosts} root/.ssh
# sed -i 's/motd=.*/noupdate/' etc/pam.d/login
# sed -i 's/1/0/' etc/apt/apt.conf.d/20auto-upgrades 
cat > etc/netplan/99-network.yaml << EoT
#network:
#  version: 2
#  renderer: networkd
#  ethernets:
#    eth0:
#      dhcp4: false
#      addresses:
#        - 192.168.1.12/24
#      gateway4: 192.168.1.1
#      nameservers:
#          search: [domain.tld]
#          addresses: [8.8.8.8, 8.8.6.6]
EoT
vi etc/netplan/99-network.yaml
# sed -i '$aNTP=ntp.domain.tld 192.168.1.1' etc/systemd/timesyncd.conf
cat > root/.aliases << EoT
unalias -a
export EDITOR=vim VISUAL=vim
export PAGER=less LESS="-FMq"
export HISTCONTROL="erasedups:ignorespace"
alias .a="vim ~/.aliases.local; . ~/.aliases.local"
alias .au=". ~/.aliases"
alias vi="vim"
EoT
ln -s .aliases root/.bash_aliases
ln -sf /usr/share/zoneinfo/EST5EDT etc/localtime
echo "myname.domain.tld" > etc/hostname
touch boot/ssh
echo "hdmi_enable_4kp60=1" >> boot/config.txt
cat > boot/wpa_supplicant.conf <<EoT
#ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
#update_config=1
#country=US

#network={
#ssid="SSID"
#psk="PASSWD"
#key_mgmt=WPA-PSK
#}
EoT
vi boot/wpa_supplicant.conf
logout
umount /mnt/rpi/boot /mnt/rpi
sync; losetup -d /dev/loop???
    Deploy image file:
lsblk | grep -v /snap
umount /run/media/*/*
echo 'pv /path/to/custom.img > /dev/device' | sudo sh
# boot the pi with the new image
usermod -L ubuntu; chage -E 1 ubuntu; passwd root