If a BCH is mined do those coins go against the total 21 million supply I wanted to find out when a fork happens does that mean there are double the amount of total coins added to the max original total of 21 million
The Bitcoin blockchain and the Bitcoin Cash blockchain are now two separate chains.  Even though they both originated from the same genesis block (and several years of common blocks), they have now forked and can never be reunited.  This means you should look at them as two separate currencies, each with their own similar but different rules.

As such, the Bitcoin blockchain can only ever support 21M BTC, and the Bitcoin Cash blockchain can only ever support 21M BCH.  So that does not mean anything has doubled; that would mean there can be 42M BTC...which isn't true.  It means there can be 21M BTC, and also 21M BCH.  Just like there may be X number of euros and X number of dollars, but that doesn't mean there are 2X euros or 2X dollars.  They are separate.