Hi @JorgeB, thanks for the prompt response, please see outputs below:
root@Phobos:~# btrfs-select-super -s 1 /dev/nvme1n1p1
warning, device 2 is missing
using SB copy 1, bytenr 67108864
root@Phobos:~# btrfs fi show
warning, device 2 is missing
Label: none uuid: 26e0b887-b92c-4df2-ae99-87f56a96103b
Total devices 2 FS bytes used 79.43GiB
devid 1 size 465.76GiB used 138.03GiB path /dev/nvme1n1p1
*** Some devices missing
root@Phobos:~#