How to Burn NFTs I've Created? What are the Conditions？

Currently, the original NFT creators can burn the NFTs they minted before they are in circulation.

Please note: Once any of the NFTs are sold, they cannot be burned.

If all the sold NFTs are returned to me, can they be burned?

Yes, when you own all versions of your work, it is also considered 'uncirculated' and can be burned.