ZH story is misleading.
Gleeson's status was not addressed by the appeals court, other than his appointment was moot.
But, as he notes, short of the Appeals Court ordering the dimissal with immediate effect, it doesn't happen until (a) the District Judge (Sullivan) dismissed it, or 21 days passes.
He (Gleeson) is under an order to respond to the district court with his brief.
So he has a conflict, and his request to the Appeals Court is valid – either tell me I don't need to file the brief, or order an extension to the filing time.
Reality is, he doesn't want to file his brief if it isn't needed, but he's under Sullivan's order to do so and Sullivan has not yet dimissed the order.
Oh, and 21 days is to allow the parties to the case to appeal – Flynn and the DOJ, and not the Judge who was a material witness in the mandamus appeal not a party.