All your permanents untap during each other playerâ€™s untap step. You have no choice about what untaps.
Other effects can prevent a permanent from untapping during an untap step. You do need to look carefully, however, as many effects say that the permanent does not untap during its controllerâ€™s untap step, and this cardâ€™s ability occurs during other playersâ€™ untap steps. If a card does say this, then Seedborn Muse can untap it. But some other abilities are not written this way and can still prevent a card from untapping.
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