Bitcoin's 21 million hard cap is built into the Bitcoin protocol and is considered one of its key features. This limit represents the maximum number of Bitcoins ever created and is intended to mimic the limited supply of a physical commodity such as gold.
Changing this hard limit will require a change in the Bitcoin protocol itself, which will require the support and consensus of the majority of the Bitcoin community, including developers, miners, and users.
Such a change would be very difficult to implement because it would fundamentally change the nature of Bitcoin and could be seen as a betrayal of the underlying principles of cryptocurrency.
The 21 million Bitcoin hard cap is embedded in the code of the Bitcoin protocol, which is what makes it scarce and valuable. Changing this will likely face significant opposition from the Bitcoin community, possibly causing a split in the network leading to a new coin.
It is worth noting that the number 21 million refers to the total number of units that can be mined, not the total amount of Bitcoin that will be in circulation. As some of the mined Bitcoins are lost, the amount of Bitcoin that will be in circulation will fall below 21 million.
In summary, changing the fixed limit of 21 million Bitcoins is highly unlikely as it would require great consensus among the community and fundamentally change the nature of Bitcoin.