So I changed the name of the community, and it was created instantly. It looks like the other mod created a community with my desired name then deleted it, but the name was still taken. I’m now a proud mod of my own community, https://lemmy.world/c/bipolardisorder. Thank you again for your help!
Yes, the group name remains with a deleted flag set. I’ve seen an admin for its home instance go in and delete them when it was brought to their attention, so that’s an option for anyone else having this issue in the future.