Wikipedia: "The Sistine Chapel is the large papal chapel built within the Vatican between 1477 and 1480 by Pope Sixtus IV, for whom the chapel is named. The ceiling was painted at the commission of Pope Julius II."

I suppose the Catholic Roman Church has always owned the chapel. It then owned the paintings as part of the chapel.

This a case where the artist was so notorious that we know he is the author. But he has never been the owner, he was paid to work.

It in fact is. The artists "just" created the works. No different from your work if you work for your employer.

It is OpenAI's GPT, not Ilya's.