BTRFS: File system unmountable, no boot and access possible

I’m sceptical, as the error message in the support database

mount: wrong fs type, bad option, bad superblock on /dev/<devicename>, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so

does not happen for me. Here’s how a try of mounting the BTRFS partition using the rescue USB looks for me:

[liveuser@eos-2021.12.17 ~]$ sudo mount -t btrfs /dev/nvme0n1p2 /mnt
mount: /mnt: mount(2) system call failed: File exists.
[liveuser@eos-2021.12.17 ~]$ 

I usually assume that the error message should match perfectly, although with newer versions of the tools messages can change.

Edit: The stacktrace looks different as well.