What exactly is there about cells that's inconceivable to replicate or synthetize? "I cannot conceive it" is a fallacy, an argument from incredulity. Trying to disguise it by draping it in the passive voice does not change that fact.

Nothing. It is just that they are so incredibly complex, that after +100 years of research we still don't know how they work or why. Will there be a time when we finally understand them 100% and could replicate them? Could be. That does not make them machines in any case, and the fallacy of thinking that mind/consciousness can emerge from machines will still be there.