Most cryptocurrencies will eventually stop being created when they reach a predetermined amount known as a mintage cap.
This is the maximum supply of the coins and the level at which no more coins will be created.
Bitcoin’s current theoretical limit is at 21 million coins by 2140. This limit is built into the technology powering the cryptocurrency, but it’s just software, and even decentralized software can be changed if the majority votes for the change.
While most cryptocurrencies have mintage caps, there are some, like Peercoin, which do not.