The church council made the recommendation in late August not to sing together indoors. This is following not only the recommendation of the UUA (the UCC has not issued such recommendations, that I am aware of). It is also in line with what we know about the delta variant. A simple, graphic illustration shows the risks associated with singing vs. gathering.
These charts come from a covid risk calculator — https://indoor-covid-safety.herokuapp.com/. The calculator allows various inputs, size of room, circulation, mask types. In both, I have used a 1500 sq foot room with 25 foot ceilings and poor circulation. The variables I have inputed are admittedly and by design conservative.