Where did you get info that Bitcoin has a 21 total of 21million coins that could ever be produced?
Simple mathematics.
The block subsidy started at 50 BTC.
Every 210,000 blocks, the block subsidy is cut in half and rounded down to the nearest 0.000000001 BTC.
210,000 blocks X 50 BTC per block = 10,500,000 BTC. Then the block subsidy is cut in half.
210,000 blocks X 25 BTC per block = 5,250,000 BTC. Then the block subsidy is cut in half.
210,000 blocks X 12.5 BTC per block = 2,625,000 BTC. Then the block subsidy is cut in half.
210,000 blocks X 6.25 BTC per block = 1,312,500 BTC. Then the block subsidy is cut in half.
If we keep up this process, eventually we reach the point where:
210,000 blocks X 0.00000002 BTC = 0.0042 BTC. Then the block subsidy is cut in half.
210,000 blocks X 0.00000001 BTC = 0.0021 BTC. Then the block subsidy is cut in half.
210,000 blocks X 0.00000000 BTC = 0.0 BTC. Then the block subsidy is cut in half.
210,000 blocks X 0.00000000 BTC = 0.0 BTC. Then the block subsidy is cut in half.
etc.
Adding up all the totals:
10,500,000 + 5,250,000 + 2,625,000 + . . . + 0.0042 BTC + 0.0021 BTC + 0.0 BTC = 20,999,999.9769
Since 20,999,999.9769 is less than 21,000,000 we can say "There will never be more than 21 million bitcoins".