If in recovery but unable to access file system, this might help - https://together.jolla.com/question/138839/how-to-run-command-from-recovery-mode/?answer=138840#post-id-138840
If I remember right, (it’s been a while since I did it), I think you don’t need the chroot part on X. Just mount Sailfish_home to /mnt, and cd to mnt and roots should be there…
Another thing that might help with a brick is fastboot flash system file from your original download zip. If the system was unmodified, it should flash back without any effect on your data…