First off, the solution to this problem is to modify /etc/tklbam/hooks.d/fixclock by adding:

from typing import Optional

And now the problem:

root@core ~# tklbam-backup
Implicit --resume: Detected a rerun of an aborted backup session
                   You can disable this with the --disable-resume option

HOOK /etc/tklbam/hooks.d/maria-db-changes :: op=backup state=pre pwd=/root ::
TKLBAM_RESTORE_PROFILE_ID:
[maria-db-changes] INFO: nothing to do when backing up
Traceback (most recent call last):
  File "/etc/tklbam/hooks.d/fixclock", line 82, in <module>
    def is_container() -> Optional[str]:
                          ^^^^^^^^
NameError: name 'Optional' is not defined
Traceback (most recent call last):
  File "/usr/bin/tklbam-backup", line 510, in <module>
    main()
  File "/usr/bin/tklbam-backup", line 439, in main
    hooks.backup.pre()
  File "/usr/lib/tklbam/hooks.py", line 78, in pre
    self._run("pre")
  File "/usr/lib/tklbam/hooks.py", line 73, in _run
    _run_hooks(self.LOCAL_HOOKS, (self.name, state))
  File "/usr/lib/tklbam/hooks.py", line 42, in _run_hooks
    (fpath, " ".join(args), e.exitcode))
hooks.HookError: `/etc/tklbam/hooks.d/fixclock backup pre` non-zero exitcode (1)
root@core ~# turnkey-version
turnkey-core-18.0-bookworm-amd64
root@core ~# ntpdate -u 192.168.3.254
2024-03-05 22:21:15.829279 (+0000) -0.006671 +/- 0.000235 192.168.3.254 s2 no-leap