Th forking (or absence of it) does not effect Bitcoin's supply. At best, you can consider it as a "gift" to all bitcoin holders, which will increase the overall worth. It in no way impacts the overall supply of 21 Mn, which is set in stone.
Yes, forking is not mean to increase the total supply but just maintenance for bitcoin like make transaction quicker for example.
Bitcoin is set only for 21 million coin and no more.
May i know what it mean bitcoin supply is set in stone? Does it mean it not possible to break it?