Balmung is hardlocked Big-C Congested, as is all of Crystal. When it was still standard was before 6.25 iirc, after that it was changed around the time they put in the new DC. It will likely stay that way until the new DCs fill up enough that will satisfy the devs. Last time Balmung was hard-locked was through all of Stormblood until Shadowbringers, but DC travel didn't exist at that point.

For now I'd say either hop to one of the new servers on the new DC (free to transfer if you're going from Balmung to a new server), or your partner can create a character there and DC travel over to Balmung to run content and then pay later to get on the server when it's back to standard. That's really the only option beyond waiting to create a character for who knows how long.