please re-read my posts regarding the question remaining, how do you know which cashed out BTC, are from which exact mined BTC.
It helps zero to know, you received x btc at x price.
You need to know, that xyz bitcoin was recieved at xx price, and those same xyz bitcoin fraction was sold at yy price.
You keep records. Then you apply these
rules. Not really that hard, especially with these high tech gadgets we have now called computahs