According to a story from the University of Notre Dame, the answer is:

the Catholic Church is the largest nongovernmental property owner in the world

While there are no numbers on the number of properties, acres, or value, I would guess that it adds up to a lot. To serve over 1.3 billion adherents around the globe – 2019 pre-Covid figures – requires a number of buildings and properties all over the place.

Asking questions about how much property a religious group should own is another matter. Is one interested in efficiency and how many people are served through each property? Is there a religious group has too much property? Does it matter if the property serves the community as well as religious adherents? All of these could factor into whether the amount of land owned is seen as a moral good or a moral problem.