What is the probability that the text between the quotation marks in this paragraph is "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce id velit urna, ac sollicitudin libero. Phasellus ac rutrum nisl. In volutpat scelerisque justo, non congue diam vestibulum sit amet. Donec."? The prior probability of this being true is minuscule, looking something like 10^-60; therefore, you might as well rule it out now.

Prior to what exactly? I do have a prior for "a randomly generated ascii string of that particular length being the same as the string given". I wouldn't be able to know to use that as the prior unless I have already been given some information. Then there is all the knowledge of human languages and cultural idiosyncracies I happen to have. Which of those am I allowed to consider? It's hard to tell since, well, you've alreay given me the answer. It's a bit post for any 'prior' except meta-uncertainty. I would need a specific counter-factual state of knowledge to be able to give a reasonable prior.

(All of which I believe supports your point.)

This seems to be a case of extraordinary claims are extraordinary evidence. It's like saying, "well yes, the fact that I have a brain is pretty extraordinary, but so what? I clearly have one". It doesn't distinguish between a Boltzmann brain and a brain arising normally via natural selection. So is your consciousness a Boltzmann consciousness?

Is it reasonable to expect me to necessarily be able to answer that question if materialism is true?

It's about as reasonable as demanding an account of how the brain can mantain mesoscopic quantum superpositions long enough to influence neural processes.

(What does the mapping from entangled quantum states to experiences look like?)

We don't know, but it's going to be far simpler than a mapping from classical brains.

(For all we know, it could be trivial; perhaps each quale is a GENSYM which maps directly to a basis of the quantum system.)