In October 2021, we had already announced the following:

"From now on the Single Sign-on type "Web Services Federation" is deprecated. From the 1st of January 2022, we will no longer support the WS-Fed SSO method in Workspace 365. However, we will continue to support this for On-Premises versions of Workspace 365".

We removed WS-Fed as authentication method for online versions of Workspace 365, but kept supporting it for existing configurations. New partners/customers weren't able to choose this authentication method anymore.

Last month, we notified the administrators to use OAuth as an alternative authentication method (only the Primary admin is allowed to configure SSO for the environment).

From next release, WS-Fed will be removed completely for online versions of Workspace 365 and it will only be available for On-Premise versions of Workspace 365.