Exchanges save permanent purchase records with the amount, date and customer's full name, photo, home address and ID scan, and they disclose these records to the state and corporations, without the customer's knowledge or permission. If you have KYC Bitcoin, the best option is to sell the same amount back to the same exchange to generate a sale record (so that the exchange and the state may assume that you don't own Bitcoin anymore).
Then buy KYC-free Bitcoin with a peer-to-peer exchange, Bitcoin ATM or Azteco voucher: https://anarkiocrypto.medium.com/how-to-buy-earn-and-spend-kyc-free-bitcoin-and-monero-without-id-or-a-bank-account-496ff20986ff
For forward privacy, you can mix Bitcoin via Whirlpool (Samourai Wallet, Sparrow Wallet) or swap Bitcoin -> Monero -> Bitcoin (use 2 different accountless exchanges and make multiple withdrawal transactions in order to avoid correlation).
There might be a proof that you bought them, but there is no way to prove that you still own them, there's always the proverbial boat accident.
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I doubt the boating accident defense would hold up in court. If they prove you bought bitcoin, you'd need to convince them you lost it, the burden would be on you at that point.
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Or you can tell them that you spent it on a trip to El Salvador. What? having some fun is illegal now?
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