https://www.denofgeek.com/tv/star-trek-deep-space-nine-breen-mystery/

The Star Trek: Discovery episode "Mirrors" includes a HUGE reveal (https://www.denofgeek.com/tv/star-trek-discovery-season-5-episode-5-easter-eggs-original-series-iss-enterprise/) about the Breen, an odd alien species from Deep Space Nine.