if anybody else has a roku TV and HBO Max (now, inexplicably, simply branded as 'max') and you get caught in the same loop I did where you launch the old app, and it tells you to go get the new app, and you do but opening that just opens the old app...
The trick is to actually *remove* the old app (highlight and then press the * button). Then you can install the new app & it will take.
@rpardee one Internet Point (TM) for referencing one of the best Simpsons episodes ever.