How to cash out a Bitcoin wallet into fiat anonymously?
If bitcoin is converted to fiat money on an exchange, the exchange has irrefutable knowledge of your identity because they require the account name and bank account name to match.

Use Bisq and other non-KYC Exchanges. Also follow the best practices mentioned in this comment:

Don't reuse addresses.

Use coinjoin and payjoin when required.

Run and use your own full node (with Tor), open source block explorer etc.

Use an open source bitcoin wallet with active development: https://bitcoinwallet.guide

Do not share information about your transactions on social media