https://www.thefenlandblackoakproject.co.uk/our-story
In particular - the section on drying - air drying would have been too rapid/harmful to the wood - so they put it into a purpose-built dehumidifying kiln for 9 months.
(It was briefly discussed here a few years ago: https://news.ycombinator.com/item?id=36912861 )
I should note he was a homesteader doing this to provide dry wood with easy access during cold months.
I’m no arborist, but I’d guess the cuts sever all of the tree’s microtubules without felling it? I think 3 would be the minimum amount of cuts you’d need.
I hadn't heard it used to get dry wood for harvesting but I recall it being useful because it actually kills the tree, so if you cut the tree down (after it's fully dead) the stump will decompose instead of trying to continue to grow.