Well, yes, i did read it too, but as far I understand, it’s not written there, neither in docs,… check edit of mailbox (as admin), there is new checkbox “Direct forwarding to SOGo After logging in, the user is automatically redirected to SOGo.” just before submit button.
If checked than login is into sogo, if not logins lands into mailcow UI both sogo and UI have buttons to go to second choise
And about /SOGo/ it should not matter unauthenticated access force redirect to /