If you’ve already gone through KYC then it’s trivial for the state to know you’re a current or past owner of bitcoin. If you can’t prove you’ve sold it they would likely assume you still have it. If you have a government that fights rather than embraces bitcoin that’s a stressful situation to find yourself in. Additionally, data leaks from hacking or a release as part of bankruptcy proceedings could reveal your address and the fact you own bitcoin. Not something you’d want to have happen.

If you’ve bought on a KYC exchange I’d recommend doing what the likes of #[4] recommend and sell through the same exchange again then buy elsewhere.

Bisq can be cheaper than a centralised exchange and have no excessive fees to withdraw either.