I seems everything in bitcoin exchanges as something that's not secret, and for we not be traced before using exchanges to convert bitcoin to fiat currency, I think we have to use mixer first and after using mixer we can transfer to exchanges, that will be less trace
I don't get your point. Can you buy bitcoin from a mixer service with fiat? However, it is not good for you to use a mixer service and send your bitcoin directly to a centralized exchange because your account would be freeze. You are also not to send directly from an exchange to a mixer.
When using a mixer, you are to send it first to your noncustodial wallet before sending it to your exchange account. It's the same when you want to use a mixer and your coins is in the exchange, you are to send first to your noncustodial wallet before sending it to a mixer.
As far as I know, centralized exchanges like Binance, Bybit... use blockchain analysis services like chainalysis, elliptic or cipherTrace. So using a noncustodial wallet as an intermediary before transferring bitcoins to an exchange or vice versa cannot guarantee that the exchange will not detect it. Using a noncustodial wallet and making a few transactions only makes it a little more complicated to track, but doesn't guarantee anything. Therefore, we need to be very careful when using mixers if we intend to transfer bitcoins to exchanges.
Instead, try combining mixers with exchanges non-KYC, or converting bitcoin to anonymous coins like XMR.
XMR is a good choice too.