Download the ISO at Ubuntu 22.04.3 LTS (Jammy Jellyfish)
Create a new folder for your custom ISO

mkdir ~/customISO

Mount the CD to /mnt

mount -o loop /path/to/ubuntu.iso /mnt

Copy the CD to your custom ISO folder

cp -r /mnt/* ~/customISO/.

Create an autoinstall folder

mkdir ~/customISO/autoinstall

Create your user-data file

vi ~/customISO/autoinstall/

You can either create a fresh file (see Automated Server installer config file reference for help) or if you already installed a system manually, you can use the same config and modify it. Its located at “/var/log/installer/autoinstall-user-data”
The meta-data doesnt need any content, just create it

touch ~/customISO/autoinstall/meta-data

Create a new bootmenu entry above all others
Make sure to match your name with “autoinstall”, “/cdrom” serves a rootdir and “autoinstall” is the directory containing your user-data file

vi ~/customISO/boot/grub/grub.cfg

menuentry "Autoinstall Ubuntu Server" {
    set gfxpayload=keep
    linux   /casper/vmlinuz quiet autoinstall ds=nocloud\;s=/cdrom/autoinstall/  ---
    initrd  /casper/initrd
}

It should look like this:

Automated Server installer config file reference
Automated Server installation - Introduction
Automated Server install quickstart
Ubuntu 22.04 Server Autoinstall ISO