[ASUS ZenFone 8] bnsmb:
It shouldn't matter, I think it's fine to download the latest OmniROM 13 image and extract the boot.img file from that ZIP file. It should also work with the latest OmniROM 14. Just give it a try - as long as you don't confirm the factory reset prompt (if any), nothing should happen to the files on the phone.

It is only important that you use the image of the boot partition from the ROM already installed on the phone.

OK, so you could use Linux commands to fix it - good.

OK; that's what I mean with "bootloader"

OK, so you installed TWRP into the boot partition

All your data files are in sub directories in /data/media/0, in an adb shell while the OS is running you need root permissions to view these files

ASUS_I006D:/ $ ls -l /data/media/0
ls: /data/media/0: Permission denied
1|ASUS_I006D:/ $ su - -c ls -l /data/media/0
total 42
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Alarms
drwxrws--x 5 media_rw media_rw 3452 2024-05-20 21:20 Android
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Audiobooks
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 DCIM
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Documents
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:24 Download
drwxrws--- 3 u0_a172 media_rw 3452 2024-05-20 21:20 Movies
drwxrws--- 3 u0_a172 media_rw 3452 2024-05-20 21:20 Music
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Notifications
drwxrws--- 3 u0_a172 media_rw 3452 2024-05-20 21:20 Pictures
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Podcasts
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Recordings
drwxrws--- 2 u0_a172 media_rw 3452 2024-05-20 21:20 Ringtones
drwxrws--- 2 root media_rw 3452 2024-05-20 21:21 TWRP
ASUS_I006D:/ $

If booted from TWRP you're always root user . But to see these directories while booted into TWRP /data must be decrypted.

Hmm, try

reboot into TWRP again and check if /data is mounted; if not, mount /data first using

twrp mount data

Check that /data is mounted and try the decrypt again.

That was the goal of that action - I did not know, that you mean bootloader when talking about fastboot.

If you already did some OTA updates; the OS in the now passive slot is also the OmniROM 13. Therefor you could also try to just copy the boot partition from the passive slot to the active slot

In an adb session while booted into TWRP do

getprop ro.boot.slot_suffix

This prints the name of the active slot, either _a or _b

If the active slot is _a do in the adb shell:

dd if=/boot/dev/block/by-name/boot_b of=/dev/block/by-name/boot_a

Or vica versa if the current slot is _b

(if = source for the copy; of = target for the copy)

To be on the safe side you could create a backup of the exsting boot partition before doing this using for example, e.g.:

dd if=/boot/dev/block/by-name/boot_a of=/tmp/boot_a.img

and pull that file via adb to the PC.

Afterwards reboot the phone from the installed OS

If that does'nt work my recommendations still stand

install a boot partition from OmniROM (either 13, or if not available from 14)

If that does not work, install OmniROM 13 (or 14 if no OmniROM 13 Image available) via TWRP . TWRP install the Image into the now passive slot and does not overwrite your existing installation.

regards

Bernd