When it comes to buying or selling crypto, one needs to make sure the trade is performed in the most private way possible.
The confidentiality of crypto transactions will decrease every year. The regulator will do its best to address this.
Just to keep governments and prying eyes away.
I wonder why the government hasn't yet come up with some kind of law "for avoiding transparency \ concealing transactions with cryptocurrencies" or something like that?

Only for the true paranoid, of course.
This isn't paranoia, but a person's legitimate right to privacy. It's sad that this right must be fought for, using various means (and not by default).
There are many ways to buy and sell crypto in a private manner. You can either trade via a DEX, F2F (Face to Face), or even a P2P trading platform. My strategy? I buy/sell BTC through a P2P exchange called Bisq, and convert some into Monero. What's yours?
Why only "some" and not all?
Your title says "crypto". So, if by "crypto" you mean XMR, then there are no privacy concerns when buying \ selling, as XMR is the embodiment of privacy.

The best private way to buy \ sell crypto is with cash. However, the need to be present in person during the transaction can be a problem (are you ready to take a risk?).
Also, your post mentions using the Bisq exchanger, which I don't think is a 100% guarantee (of course not) of privacy, and any other exchanger could be used. This isn't crucial. After this step, should probably add a bitcoin mixer and then convert the received BTC to XMR. Which one should you exchange for cash at the exchanger? At each step, you'll lose some in fees. Maybe it's easier to pay taxes to the government?

By the way, why hasn't the government yet "banned" the use of XMR (and similar coins), perhaps under threat of criminal liability? After all, that's a valid reason if can't control or track transactions.