This is adapted from the Debian bookworm instructions for ZBM

Do not choos to immediately reboot after applying an update. You need to add the pass phrase to the initrd of the new TrueNAS version. Connect to the admin account on the TrueNAS system using SSH:

sudo -s
export ID=<new release version>
mkdir -p /mnt/update
mount -t zfs boot-pool/ROOT/${ID} /mnt/update
mount -t proc proc /mnt/update/proc
mount -t sysfs sys /mnt/update/sys
mount -B /dev /mnt/update/dev
mount -t devpts pts /mnt/update/dev/pts
mount boot-pool/grub /mnt/update/boot/grub -t zfs
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/audit /mnt/update/audit
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/data /mnt/update/data
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/etc /mnt/update/etc
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/home /mnt/update/home
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/mnt /mnt/update/mnt
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/opt /mnt/update/opt
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/root /mnt/update/root
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/usr /mnt/update/usr
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/var /mnt/update/var
mount -t zfs -o zfsutil boot-pool/ROOT/${ID}/var/log /mnt/update/var/log
cp /etc/zfs/boot-pool.key /mnt/update/etc/zfs/boot-pool.key
chmod 000 /mnt/update/etc/zfs/boot-pool.key
chroot /mnt/update /usr/bin/zsh

You are now in the new TrueNAS system version:

echo "UMASK=0077" > /etc/initramfs-tools/conf.d/umask.conf
update-initramfs -c -k all
exit

You can clean up now:

umount -R /mnt/update
rmdir /mnt/update

Reboot and the system should ask you for the pass phrase and then the new version should boot as ususal.

You will end up in initrd recovery. You can enter the pass phrase and mount root to continue:

zfs load-key -a
# boot-pool: <password>
mount /boot-pool/ROOT/<version> /ROOT
exit

The TrueNAS scale system will now boot. To make the pass phrase permanent you have to write it to the intird:

mount / -o remount,rw
echo 'TestMeHard' > /etc/zfs/boot-pool.key
chmod 000 /etc/zfs/boot-pool.key
echo "UMASK=0077" > /etc/initramfs-tools/conf.d/umask.conf
update-initramfs -c -k all

Start an SSH session with the admin account:

sudo -s
# Enter admin's password
export ID=$(cat /etc/version)
# for sdx drives
export BOOT_DISK="/dev/sdx"
export BOOT_PART="2"
export BOOT_DEVICE="${BOOT_DISK}${BOOT_PART}"
export POOL_DISK="/dev/sdx"
export POOL_PART="3"
export POOL_DEVICE="${POOL_DISK}${POOL_PART}"
# for NVMes
export BOOT_DISK="/dev/nvmeOn1"
export BOOT_PART="2"
export BOOT_DEVICE="${BOOT_DISK}p${BOOT_PART}"
export POOL_DISK="/dev/nvmeOn1"
export POOL_PART="3"
export POOL_DEVICE="${POOL_DISK}p${POOL_PART}"
 
echo '<A good passphrase, you will need to type this with en_US keyboard layout just after UEFI>' > /etc/zfs/boot-pool.key
chmod 000 /etc/zfs/boot-pool.key
# the pass phrase is now in an unencrypted part of the system
# follow through with these instructions and it will be encrypted on rest (power off)
 
# Change one of the mirrored boot devices to an encrypted boot-pool
zpool detach boot-pool "$POOL_DEVICE"
zpool labelclear -f "$POOL_DEVICE"
 
zpool create -f -o ashift=12 \
 -O compression=lz4 \
 -O acltype=posixacl \
 -O xattr=sa \
 -O relatime=on \
 -O encryption=aes-256-gcm \
 -O keylocation=file:///etc/zfs/boot-pool.key \
 -O keyformat=passphrase \
 -o autotrim=on \
 -o compatibility=openzfs-2.1-linux \
 -m none boot-pool-enc "$POOL_DEVICE"
 
zfs create -o mountpoint=none boot-pool-enc/ROOT
zfs snapshot -r boot-pool/ROOT/${ID}@transfer
zfs snapshot -r boot-pool/grub@transfer
zfs send -pRP boot-pool/ROOT/${ID}@transfer | zfs recv -d -o encryption=on -x keyformat -x keylocation boot-pool-enc
zfs send -pRP boot-pool/grub@transfer | zfs recv -d -o encryption=on -x keyformat -x keylocation boot-pool-enc
zfs set org.zfsbootmenu:active=on boot-pool-enc/ROOT/${ID}
zpool set bootfs=boot-pool-enc/ROOT/${ID} boot-pool-enc
zpool export boot-pool-enc
 
# necessary changes for booting without the pass phrase
zpool import -N -R /mnt/enc boot-pool-enc
zfs load-key -L prompt boot-pool-enc
mkdir -p /mnt/enc
mount boot-pool-enc/ROOT/${ID} /mnt/enc -t zfs
mount -t proc proc /mnt/enc/proc
mount -t sysfs sys /mnt/enc/sys
mount -B /dev /mnt/enc/dev
mount -t devpts pts /mnt/enc/dev/pts
mount boot-pool-enc/grub /mnt/enc/boot/grub -t zfs
zfs mount boot-pool-enc/ROOT/${ID}/audit
zfs mount boot-pool-enc/ROOT/${ID}/data
zfs mount boot-pool-enc/ROOT/${ID}/etc
zfs mount boot-pool-enc/ROOT/${ID}/home
zfs mount boot-pool-enc/ROOT/${ID}/mnt
zfs mount boot-pool-enc/ROOT/${ID}/opt
zfs mount boot-pool-enc/ROOT/${ID}/root
zfs mount boot-pool-enc/ROOT/${ID}/usr
zfs mount boot-pool-enc/ROOT/${ID}/var
zfs mount boot-pool-enc/ROOT/${ID}/var/log
chroot /mnt/enc /usr/bin/zsh

You are now in a shell in the copied, encrypted TrueNAS system

echo "UMASK=0077" > /etc/initramfs-tools/conf.d/umask.conf
update-initramfs -c -k all
exit

Install ZBM in the EFI partition (ZBM does not support secure boot, it is not signed)

mount ${BOOT_DEVICE} /boot/efi
mkdir -p /boot/efi/EFI/ZBM
curl -o /boot/efi/EFI/ZBM/VMLINUZ.EFI -L https://get.zfsbootmenu.org/efi
cp /boot/efi/EFI/ZBM/VMLINUZ.EFI /boot/efi/EFI/ZBM/VMLINUZ-BACKUP.EFI
efibootmgr -c -d "$BOOT_DISK" -p "$BOOT_PART" \
  -L "ZFSBootMenu (Backup)" \
  -l '\EFI\ZBM\VMLINUZ-BACKUP.EFI'
 
efibootmgr -c -d "$BOOT_DISK" -p "$BOOT_PART" \
  -L "ZFSBootMenu" \
  -l '\EFI\ZBM\VMLINUZ.EFI'
umount ${BOOT_DEVICE}

Unmount the encrypted TrueNAS System

umount -R /mnt/enc
# You can remove the snapshots created to copy the TrueNAS System
# zfs destroy -r boot-pool/ROOT/${ID}@transfer
# zfs destroy -r boot-pool/grub@transfer
# zfs destroy -r boot-pool-enc/ROOT/${ID}@transfer
# zfs destroy -r boot-pool-enc/grub@transfer
zpool export boot-pool-enc
reboot

This can be done in the ZFS Boot Menu Rescue shell after the reboot. The commands need to be typed with en-US keyboard layout

zpool import -f boot-pool boot-pool-old
zpool export boot-pool-old
zpool export boot-pool-enc
zpool import boot-pool-enc boot-pool
reboot

Unlock and start TrueNAS. If it works as expected convert the second mirror boot device to a mirror device for the now encrypted boot-pool. Again open an SSH connection as the admin user:

sudo -s
export ID=$(cat /etc/version)
# for sdx drives
export BOOT_DISK="/dev/sdy"
export BOOT_PART="2"
export BOOT_DEVICE="${BOOT_DISK}${BOOT_PART}"
export POOL_DISK="/dev/sdy"
export POOL_PART="3"
export POOL_DEVICE="${POOL_DISK}${POOL_PART}"
export CURRENT_POOL_DISK="/dev/sdx"
export CURRENT_POOL_PART="3"
export CURRENT_POOL_DEVICE="${CURRENT_POOL_DISK}${CURRENT_POOL_PART}"
# for NVMes
export BOOT_DISK="/dev/nvmePn1"
export BOOT_PART="2"
export BOOT_DEVICE="${BOOT_DISK}p${BOOT_PART}"
export POOL_DISK="/dev/nvmePn1"
export POOL_PART="3"
export POOL_DEVICE="${POOL_DISK}p${POOL_PART}"
export CURRENT_POOL_DISK="/dev/nvmeOn1"
export CURRENT_POOL_PART="3"
export CURRENT_POOL_DEVICE="${CURRENT_POOL_DISK}p${CURRENT_POOL_PART}"
 
zpool labelclear -f "$POOL_DEVICE"
zpool attach boot-pool "$CURRENT_POOL_DEVICE" "$POOL_DEVICE"
 
# now also add ZBM to the second EFI partition
mount ${BOOT_DEVICE} /boot/efi
mkdir -p /boot/efi/EFI/ZBM
curl -o /boot/efi/EFI/ZBM/VMLINUZ.EFI -L https://get.zfsbootmenu.org/efi
cp /boot/efi/EFI/ZBM/VMLINUZ.EFI /boot/efi/EFI/ZBM/VMLINUZ-BACKUP.EFI
efibootmgr -c -d "$BOOT_DISK" -p "$BOOT_PART" \
  -L "ZFSBootMenu (Backup)" \
  -l '\EFI\ZBM\VMLINUZ-BACKUP.EFI'
 
efibootmgr -c -d "$BOOT_DISK" -p "$BOOT_PART" \
  -L "ZFSBootMenu" \
  -l '\EFI\ZBM\VMLINUZ.EFI'
umount ${BOOT_DEVICE}