I've updated the "status" of the epic to be "done", but it has not fallen off my backlog's epic panel (weirdly, I thought it HAD fallen off previously, but is suddenly back.... bug?...).
I see other posts about this, but they aren't helpful since they all reference changing the "epic status" field to "done", but I don't see that anywhere... not in the epic details on the backlog, not in the epic details when I bring up the full page epic, and not in the configuration settings for epics.