Earlier quoted context omitted.
Any publication is fine as long as you can provide evidence. In fact the only thing special about publication is that it is a convenient way to demonstrate evidence of the prior art. What could be tricky about e.g. a personal blog post is proving that it was published when you say it was and that time stamps are genuine.
For those who are interested and doesn't know already[0] this is one of the places where blockchains and similar, older technoologies are actually useful: to provide irrefutable proof of knowledge at a given time. Note however that similar services has been done for years[1] before Bitcoins and blockchains became a thing but since they neither need multi-Gigawatt-Proof-of-Work [2] nor any kind of "Coin" that can be p…
The internet archive has long been used as evidence for such publication-at-time claims, and they even have a paid service allowing you to trigger snapshots IIRC. There's a FAQ regarding the use of their data in court cases that is somewhat interesting to read.
I know the cryptocurrency community has this absurd notion that nothing without cryptographic proof could or should ever be regarded as evidence. That trusting institutions, people, or processes marks you as a gullible fool, and that the Federal Reserve is conspiracy by private banks to keep the gentile from the levers of power[0].
So this is the not entirely novel situation of crypto being proposed to solve a problem that doesn't exist, and failing due to the lack of (usually: active hostility to) subject matter expertise.
[0] last point unrelated to this specific situation and just included for completeness