Coin type hand exchange always happens every day on the exchange. You exchange BNB for USDT, the exchange will verify your request, that's when the coin transfer process occurs. Just like the BTC exchange process, every day there is demand and supply, in simpler terms to make it easier for you to understand this process. When you buy Bitcoin there is always someone selling it.
Bitcoin rotation will always be on its axis, the exchange process will continue as long as Bitcoin can still be exchanged.
You are totally right, but you should also shed light on when there are fewer buyers or sellers, let's say if a person wants to sell BTC but there is no buyer then who he will sell them? Every exchange has its own liquidity pools or proof of reserves which shows that they can process big trades easily.
For example, if the pool has a limit of 10 BTC then trade with bigger than 10 BTC has to wait. Until the pool size increases or until there come buyers for the deal worth 10 BTC.
Another confusion I have is about BTC.
BTC has a total supply of 19,495,156 million. Now the entire 19,495,156 are in circulation which means they are being held by holders/users. But another user can always swap another coin to BTC at anytime and receive the BTC, so where is the BTC coming from since it already in circulation (held by other holders)?
The total supply of BTC is 21 million and the circulating supply is the one which you have mentioned above, and despite the holders and users or traders, BTC will be tradeable until their is a buyer or seller and the pools which are keeping the books clean and unstoppable. Some users have shed light on the pools even tranthidung mentioned some useful threads for you to read.
there
I suggest you read them fore a better understanding.