Both. If you're the player with the Seedborn Muse , you'll have a limited untap during your own untap step. However, Seedborn Muse will give you an untap during the other player's untap step, which is not restricted by Winter Orb or Static Orb because it's not your untap step (both Orbs clearly say "during their untap step").
July 4, 2021 12:18 a.m.
Polaris, thank you, very much; that information shall be most helpful.