Any clue what's causing this ?
Linux 5.15+ removed support for NTLM: https://git.kernel.org/pub/scm/linux/…782eb68f61a179c
There was some discussion about reverting the change but Linus rejected the idea https://lore.kernel.org/all/CAHk-=wjSB…mail.gmail.com/ and a simple git revert no longer works due to surrounding code change in the kernel.
Some workarounds are mentioned in https://bugzilla.kernel.org/show_bug.cgi?id=216682; AFPS support via FUSE is probably the right direction to move in. The original AFPS project looks to be quite dead but https://github.com/Netatalk/netatalk-client seems to be current and might be something we can package into an installable add-on similar to NTFS-3G.
I still have a TimeCapsule in a box somewhere, but I'm travelling and it will be a ~week before I can investigate further.