Someone made a mirror of the docker server: https://hub.docker.com/r/ericreeves/ferdi-server/
Also this is a fork of the fork: https://github.com/pacstah/ferdium
And the WayBackMachine for the github: https://web.archive.org/web/20220313212244/https://github.co...
Some users are saying that you can logout, delete and re-add all the services, then it works again: https://www.reddit.com/r/getferdi/comments/u2swcs/you_can_st...
Finally, you can dnownload Ferdi here and set the server to Franz, it's supposed to work too: https://sourceforge.net/projects/ferdi.mirror/