A seated imam may perform actual bowing and prostration, so Abu Hanifa and Abu Yusuf permit a standing follower behind him.
An imam using gestures instead of bowing and prostrating is a different case: the usual Hanafi ruling disallows following him for someone able to do those acts, though Zufar differs.
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Whom May One Follow in Prayer? Qualifications and Validity of Imamate
A seated imam may perform actual bowing and prostration, so Abu Hanifa and Abu Yusuf permit a standing follower behind him.
An imam using gestures instead of bowing and prostrating is a different case: the usual Hanafi ruling disallows following him for someone able to do those acts, though Zufar differs.