Microsoft has reportedly removed the $1
Game Pass Ultimate offer from its storefront, Twitter users are
currently reporting, and this can be confirmed by a
visit to the store itself. The deal allowed you to get access to the first month of the subscription service for one dollar, and then pay $15 for each subsequent month if you wanted to keep the subscription active.
It's not really a drastic change, as this offer only affects those who are new to Game Pass Ultimate. It is highly plausible that this was done to combat those who subscribe to Game Pass
via the Gold workaround.