1 disk RAID failed in NSA320S

Hello,

I have a NSA320S (Firmware: V4.70(AANV.0)), I had some hard times with it, but Mijzelf always helped.
So now, after a power failure it cannot boot, no sign of life.

I've removed the disk (4TB Seagate) and plugged it into a Rasberry PI via USB adapter. Previously I had HDD problems, so I made notes, how to mount this type of HDD into linux on RPi, so I started with:

$ sudo fdisk -l /dev/sdb
Disk /dev/sdb: 1,7 TiB, 1801763774464 bytes, 3519069872 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device Boot Start End Sectors Size Id Type
/dev/sdb1 1 4294967295 4294967295 2T ee GPT

This is weird, because last time it reported 2 devices: sdb1 & sdb2

In my notes, the next command is:
$ sudo mdadm --assemble --run /dev/md0 /dev/sdb2

it also not works, because of missing sdb2 device.

I also tried this:
$ sudo mdadm -E /dev/sdb
/dev/sdb:
MBR Magic : aa55
Partition[0] : 4294967295 sectors at 1 (type ee)

$ sudo mdadm -E /dev/sdb1
mdadm: cannot open /dev/sdb1: No such file or directory

After this failed attempts I've plugged the disk into a Win11 machine to watch the partition tables.
It shows 2 partitons: a 487 MB and a 3814959 MB one. The disk contains a Guid Partition Table (GPT).
I've tried a disk recovery software, too, it can show my files in bulk (without the directory structure), so it is nearly useless.

Is it possible to fix it to use the NAS again?
I thik this is my last effort to exted my Zyxel NAS' lifetime :-(

Thank you!