I'm not familiar with South Korean church practices, but there is an instance of a choir practice in the US that spread COVID-19 fairly effectively. This suggests that singing, a common practice in US churches (in my experience), spreads the disease. An article on the event reports that the choir members attempted to distance themselves from each other and use hand sanitizer.
https://nypost.com/2020/03/30/washington-choir-rehearsal-tur...