However, I'd like to know if there will be BTC miners once the supply is fully mined, and will the fees for sending from wallets to exchanges be high? I also wonder if the price fluctuations will be similar to the current bearish and bullish market. Currently, BTC is widely traded, buying at a low price and selling at a high price. But will BTC trading be possible in the future, similar to daily trading? I think this is worth discussing... 
There is, as long as the transaction keeps going.
The cost depends on how congested the network is.
It depends on the law of supply and demand regarding price fluctuations.
The scarcity of Bitcoin once the total supply is reached will have a positive impact on the price, which is expected to get more expensive and of course all things that will happen to Bitcoin in the future I say based on speculation, not certainty.
Do more research before jumping to conclusions.