Normally we sing in parallel, everyone at once. We're all in the same room, so the time from when you make a sound to when I hear it is very small compared to the speed at which we perceive music. Since we're currently avoiding being close to each other, however, there's now too much delay to make traditional parallel singing work. This is hard since it's a time we'd especially like to be able to sing together.
One potential solution is circular singing. Pick a song which works with a fixed delay, and then I hear you following me while you hear me following you. I was musing about singing rounds this way a few years ago, but it looks like there have been open source implementations of this going back to at least 2005 there's a hosted service.
Another approach, though, would be series singing, like a bucket brigade. You have a leader who sings/plays and hears only themself, and each person in the chain hears everyone before them. This seems like it could be a good fit for churches especially? Has anyone tried this, or seen anything like it?