So you clicked the "other options" button? I am surprised that is still showing if you did click it.
To me this is suggesting that the "unknown error" is something else. Of course it isn't very helpful other than saying it is unknown. For unknown error issues I suggest you contact Apple and see if they know.
Incidentally, I do not use two factor and I have Sequoia like you. I have not tried signing out of my account recently just to see what happens (and would prefer not to, I am sure you understand).
Two suggestions: Make sure your using the most recent Sequoia, and also try simply restarting your computer and if that takes care of the issue. I have encountered a bunch of Sequoia issues where restarting an application or even the entire system resolved an issue.
Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page under “Get more help” (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple Support - Apple Support For some countries look under “Other” listing at the end of the list. Not every country has telephone support, and phone numbers may only work when calling from the same country.
Note that Apple probably won't help you with any issues related to security questions at all, but to me this looks like security questions is not the issue here.