It's very simple and unavoidable. He was baptised a Catholic, and was never excommunicated.
Whatever speculations you might produce from "historians" who could not know what he thought, the fact of his religion remains.
Those historical "speculations" are drawn from what he wrote and said. You should investigate that before spouting nonsense.
One is baptized shortly after birth way before any sense of choice develops. I was baptized, etc, but am an atheist.
Tradition is not the worship of ashes, but the preservation of fire. ― Gustav Mahler
There are a plethora of places where you can verify these numbers, if you care to do so. Mao Ze-Dong (China, 1958-61 and 1966-69, Tibet 1949-50) 49-78,000,00 people murdered Jozef Stalin (USSR 1932-39 only) 15,000,000 people murdered Pol Pot (Cambodia, 1975-79) 1,700,000 people murdered Kim II Sung (North Korea 1948-94) 1.6 million people murdered Tito (Yugoslavia 1945-1987) 570,000 people murdered Suharto (Communists 1967-66) 500,000 people murdered Ante Pavelic (Croatia 1941-45) 359,000 people murdered Ho Chi Min (Vietnam 1953-56) 200,000 people murdered Vladimir Ilich Lenin (USSR, 1917-20) 30,000 people murdered Adolf Hitler (Germany 1939-1945) 12,000,000 people murdered