Unable to boot after update from within auto-admin

Hi, I'm very new to FreeBSD.

Everything was working fine on my (desktop) system for a few days when I received a popup notification from within Openbox that updates were ready. I was skeptical so I closed the popup box and it said I could run 'auto-admin' at any time. I tried running auto-admin after logging out of Openbox and user session, logged in as root, selected the update option from the menu, it ran it, I accepted the reboot option, and I cannot boot into my system.

I'm running FreeBSD 15, on an old laptop with old BIOS. (from 2010 or thereabouts) I'm not compiling software, just using snapshot packages as selected during the install. I used the guided disk installer option. My system was up-to-date as far as I know prior to this.

Up to this point I'd been updating my system with pkg update then pkg upgrade and it's been smooth, but this popup led me to an update process in auto-admin which hosed my system.

Here are the error messages at boot, after I enter my encryption pass:

---
Can't find /boot/zfsloader
Can't find /boot/loader

zio_read error: 5
zio_read error: 5
zfs: i/o error - all block copies unavailable
zfs: can't read object set for dataset 388
zfs: can't open root filesystem
can't find /boot/kernel/kernel

freebsd/x86 boot
default:zfs:zroot/ROOT/default:/boot/kernel/kernel
boot:
---
I searched the web for instructions, and came upon something which I tried:

- Boot from FreeBSD 15 LiveDVD

- Choose Single User and login as root

- gpart show

- gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0

(after using gpart show -l and gpart -p to verify freebsd-boot location)

It displayed the text that it was written and I rebooted and the system still throws up the errors after entering my encryption password.

I don't know what else to do at this point other than a complete reinstall, which would be a hard lesson to learn as I haven't saved any backups of personal files. I didn't expect this would hose my system. Was I correct to run the update as suggested via auto-admin then reboot? Is this type of popup notification normal?

I'm quite the BSD newbie. I tried to research this and fix it myself but.. I failed.

Is there any way to salvage the installation at this point?