It depends on Duplicati version, which is in a transition period.
Release: 2.1.0.2 (Beta) 2024-11-29
The new password requirement compared to prior Beta is the middle item.
Communicating this with Docker users seems to be especially challenging.
https://hub.docker.com/r/duplicati/duplicati
chose to describe the new scheme, although old Dockers are still available.
New directions should work with old Docker from a password point of view.
https://hub.docker.com/r/linuxserver/duplicati
shows method that works on old and new, but password is required on new.
Empty password used to clear password (after a set), but that’s now denied.
IMO LSIO should update their doc to new requirement, but that’s up to them.
I’m glad you got it working.