focus using only decentralized exchange such as "bisq.net" which supports only desktop, and both buying and selling of Bitcoin.
Do you mean using a help of Japanese mother? be sure you're open the site first before recommend to anyone else or maybe you're don't know what is Bisq and only follow what above users were posting.
You want privacy, at the very least use privacy coins like Monero.
It's true Monero offer a good privacy, but the @OP asking about how to use Bitcoin for privacy. Monero future journey might be not bright because more and more centralized exchanges delist this coin.