Where can I read more about this? If this was a fact I think people would be way more excited about cryonics. Casually browsing wikipedia suggests that we are not there yet with the ability to thawn large animals or even organs.

From https://en.wikipedia.org/wiki/James_Lovelock

"In the mid-1950s, Lovelock experimented with the cryopreservation of rodents, determining that hamsters could be frozen and revived successfully.[14] Hamsters were frozen with 60% of the water in the brain crystallised into ice with no adverse effects recorded. Other organs were shown to be susceptible to damage.[15]"

And there's a Tom Scott's interview with James Lovelock:

https://www.youtube.com/watch?v=2tdiKTSdE9Y

Wouldn’t it be crazy if only worked on hamsters

I can't source this because I read it years ago, but I believe that there is some science that says that a major factor (not the only major factor, but a major factor) is body mass and volume. Essentially, the speed at which the core organs go from operating temperature to frozen is crucial, and it's also important for them to be deprived of oxygen when that happens. Humans are just... too big.

There are ways to adjust cooling rates... for example route the blood externally and chill it like they do in some kinds of surgery.

I was checking youtube to see if I could see that happen but failed - they were all about thawing rats to feed to snakes. There was however a goldfish dropped in liquid nitrogen briefly and recovering https://www.youtube.com/watch?v=wwolYFGM9pU

These experiments are exactly why people were excited about cryonics, until they realized that it doesn't work on anything much larger than a rat.

You have to thaw them right down to the core very quickly; you need to get the heart pumping or the thawed extremities will die with no bloodflow. There's no way to heat a human's core that fast without causing unsurvivable burns to their outside. (Even the rats wound up with nasty, sometimes fatal burns.)