How is the ExtraNonce calculated in Bitcoin Core The Extra nonce for the genesis block in bitcoin core is 0x010445, how was this value calculated?
The extra nonce is just like the normal nonce in a block header. It is "calculated" by using a counter which increments every time all of the possible nonces for the block header nonce field are exhausted. This process of incrementing the nonce and then the extra nonce is repeated until a valid block hash is found.