In the 2040s, the Protestant sect of Christianity is almost nonexistent. The Amish, and Mennonites being the exception. Those communities are stable, and growing.
Both traditionalist & Vatican 2 Catholicism are doing just fine. They’re definitely stable but growth is hit or miss. It really depends on where you are.
The Mormons have reverted to their 19th century ideals. The Mormon Church is strengthening it’s hold on the Northwest. It’s also making an effort to take the Midwest. However there’s some competition there.
Islam is also trying to become the dominant belief system of the American Midwest. So it’s a Mormon versus Muslim battle for the soul of the region. With Mormon men being permitted to have two wives.
They are doing well in Illinois, Minnesota, Ohio, and parts of Michigan. This is a slightly moderate return to their polygamist roots. A purely tactical move I’m sure. However Islam countered by telling Midwestern men that they can have four wives.
Street gang style territory battles would begin after this.
California became aggressively anti-theistic.
The Southwest embraced Folk Catholicism, and New Age star seed spirituality.
The Northeast became the land of the witches. Wicca, Hinduism, and European polytheism became the Northeast’s religious Big 3. While Catholicism maintain a steady hold on Boston, and parts of New York City.
New Jersey is a religious melting pot, and every faith wants to be number one. Christianity, Islam, Hinduism, Sikhism, and so on. The streets can be dicey at times.
Louisiana, and Florida embraced Afro-Caribbean religions. While the rest of the South is witnessing the birth of a strange new church. It’s Baptist Christianity mixed with Discordianism.
Las Vegas believes in a very pro-hedonism, and hyper-capitalist variant of Scientology.
Hawaii & Alaska believe in Zoroastrianism.
The remaining Protestants have begun purchasing land in Botswana. They plan to create a futuristic gated city that follows the beliefs of Martin Luther & John Calvin. Only Protestants born on American soil will be permitted to live there.
Islam & Mormonism in America merged into one brand new syncretic religion by 2062.