Yes it is true that many bitcoins have already been lost.  Many bitcoins have been locked due to unconsciousness And if Bitcoin has a specific supply then why isn't Bitcoin growing much? This is because Bitcoin has not yet spread to everyone.

It is estimated that only 3.9-4% of people worldwide use crypto from 100%.  And with approximately 18,000 businesses accepting crypto. The Bitcoin prices have risen 540,000% from btc release since only 4% of people worldwide use cryptocurrencies.  Bitcoin has reached an annual growth rate of 274% So have you ever wondered what the price of Bitcoin would be if 50% of people worldwide use Bitcoin?