Can I sell an NFT I minted here?

Yes. NFTs minted on this site are on Creta's own contract, which is enabled for auctions — so they list like any other Creta item: My NFTs, choose the item, set a starting price, approve and list.

Whether anyone bids is a separate matter. Minting makes an item sellable; it does not give it a value, and nobody at Creta can promise one.