Was able to join a freeform commander game with Tasha, the Witch Queen in the command zone in addition to the Golos, Tireless Pilgrim of my testing deck, but when I swapped my Talion, the Kindly Lord out for Tasha, the Witch Queen and tried to start a solitaire game I received an error. So something does seem off when Tasha, the Witch Queen is your commander in the regular commander room.