As there are a lot of people who are quite opposed to Bitcoin/PoW/blockchain/etc, I assume if it was true, someone would have come up with some indisputable, solid evidence for it, and it would make the tech news rounds for quite some time (there are enough anti-Bitcoin writers and commenters that such a thing would never die, and would be brought up with some links to the evidence in literally every article written about Bitcoin).
As that's not happened, I remain inclined to treat it as rumors and "But if you use this OTP you can get the following out!" sort of trickery.