I never even noticed the fee, it's ridiculous, something like 1 dollar or 3 dollars.

There is no way to avoid fees. However, it is possible to negotiate at much lower brokerage fees. There is also the smart method of converting Fiat only at the right time, the time that is most convenient for you.
Let's give an example that I just saw here.
Buy Bitcoin with Real.
“One day you have R$1000 and decide to buy some Bitcoins, make a trade and withdraw the results.” Ok? That’s the example.
Convert Fiat BRL to BNB when BNB is low.

Trade Bitcoin with BNB pair.