It needs to be their Primary group for this TC to kick in. That is by design, so that there is no conflict when a user is a member of more than one group with a redirect.
Our logic at the start was that it only overrides the default homepage - all others (including anon) take precedence.
The classic use case is using the Categories + Latest view on desktop, as this displays as Categories on mobile (which isn’t very useful).
These days, the sidebar makes this unnecessary for most instances, so I think that removing it makes sense. It might catch out some who have been using the TC for a while though.