In his commentary on Taittriya Upanishad Sankara (Tai.Up. I.xi.4),during his discussion of Karma, Knowledge and Liberation, proffers three contraposititions to his doctrine of the central importance of Knowledge in the achievement of Liberation. These objections centre on orthopraxis which is a feature of the religion in its Mere Hinduism form to borrow a phrase. That ancient strand of the primacy of ritual is moderated by the Upanishads’ discussion of the inner symbolic meanings of fire, ghee etc. Sankara takes a rigourist view of Knowledge as the sole factor in the banishment of ignorance. Is the ascription the book Soundarya Lahari with its detailed description of Yajna, Yantra and Mantra to him an attempt to bring him back to ritualism? Who can say at this point. If you google 'yajna’ you will be offered them for a fee of 900$. For the finding of a suitable life partner cheap at the price.
To summarise his rebuttals: it’s all karma/action and only brings more karma in its train.
And hence liberation is not (an) achievable (result). A traveller has to reach a place which is different from himself. Not that the very place that is non-different from himself can be reached by ones self. And this follows from the well-known fact of identity (of the individual and Brahman) gathered from hundreds of Vedic and Sruti texts such as “Having created it (the world ), He entered into it”. *(Tai.Up. II.vi.1), “Know the individual soul also to be myself” (G. XIII.2).