The limit of 21 Million is set in the code which can only be changed with a hard fork, which would require agreement of the community.
The limited supply of 21 Million is the core strength of Bitcoin, and that is the reason it is considered anti-inflationary and hedge against fiat currencies.
This kind of forking will be hard since we need a consensus of 95% and with the number of bitcoin adopters increasing daily it will not be easy to achieve. Lets take the bitcoin diamond hard forked form the blockchain for example, it was supposed to address the 21 million limit of bitcoin and it was increased 10 times (210 million) but today the price signifies that bitcoiners do not accept this kind of consensus. So even in future I doubt there will be a fork that will actually solve this limitation problem because it is one of the most important factors that makes bitcoin unique.
The next halving will take place in 2024 and with that the mining reward will reduce to 3.125 bitcoin per block and the halving will continue in that way after every four years until it reaches the end at year 2140. Just imagine what will be the expected price of a Bitcoin in that year. Those who invest in Bitcoin today would have rich generations with that investment.
To explain more, the bitcoin blockchain adds new block every 600 seconds (10 minutes) and after 210,000 blocks have been added it is when the reward is halved which is approximately every fours years.
What some people are worried about is that the transaction fee will not be enough for miners when bitcoin mining fees stop coming. Yes today the fees are not that high but with bitcoin adoption growing fast before 2140 there will be more people using bitcoin for daily transactions which will significantly increase the fees. Also not many of the current miners will still continue as the cost of mining is getting expensive daily