In Star Trek: Discovery season 5, episode 5, “Mirrors”, Detmer and Owosekun were assigned to pilot the Mirror Universe’s ISS Enterprise to Federation HQ by Captain Michael Burnham (Sonequa Martin-Green). This explained Detmer and Owo’s absence for the rest of Discovery season 5.
However, Detmer and Owo do appear in Star Trek: Discovery’s epilogue scene, and they were a sight for sore eyes.
I think it was a worthy experiment - take the nameless, silent extras that populate the bridge on the older shows and give them a little more to do.
But I think it created some unintended and unfortunate audience expectations. Maybe a failed experiment.
I would imagine none of those actors were under contract.