"Forgot" Password

I would hope a --server-datafolder=/config/duplicati would persuade it.
That’s deeper than I would have thought. Are you using a LinuxServer image?
The image Duplicati supplies puts its databases under /data. Useful reading:

Using Duplicati from Docker but LSIO did a few things differently in their image.

You might want to printenv to see what’s set now. Read your own config too.
Anyway, Duplicati usually uses $HOME/.config/Duplicati unless overridden by:

--server-datafolder: Duplicati needs to store a small database with all settings. Use this option to choose where the settings are stored. This option can also be set with the environment variable DUPLICATI_HOME.

and I found a dev post saying DUPLICATI__SERVER_DATAFOLDER variable can move it.
I think I’ve run the option format, but if it doesn’t, try the environment variable instead.