I tried moving
Apple Account / App Store regions, but this apparently required all subscriptions to have ended to core Apple services like Apple Music and Apple TV+, but curiously, not iCloud Plus. After disconnecting Apple TV+ from my
T-Mobile account, I learned that in-practice, Apple immediately moves you to a subscription and charges you. This led me to contact Apple Support. Apple Support claimed that they would cancel and refund me, allowing me to change regions within 2 hours. However, this turned out to be false. It took about two days for me to get the region change function.