NFTs are just crypto that isn't divisible.

Basics:

https://www.reddit.com/r/btc/wiki/index

Blocksize debate:

https://www.reddit.com/r/btc/comments/js6jft/frequently_asked_questions_and_information_thread/

https://medium.com/@johnblocke/a-brief-and-incomplete-history-of-censorship-in-r-bitcoin-c85a290fe43

https://medium.com/@johnblocke/r-bitcoin-censorship-revisited-58d5b1bdcd64

Starting point for other chains (let’s face it, the good guys lost the blocksize debate and BCH isn’t next in line, so the next best thing for NFTs is Ethereum):

https://ethereum.org/en/learn/