full disk encryption Ubuntu install scripts, from https://help.ubuntu.com/community/Full_Disk_Encryption_Howto_2019
run sh pre-install.sh before running installer
follow the installer, selecting the appropriate mount points, including the boot partition as described here
run sh install.sh after all configurations in installer are completed and immediately after installation begins
run sh chroot.sh then mount -a then run sh post-install.sh after installer has completed install, but before reboot