You can easily sell them mostly on the NFT marketplaces like opensea. It's the most known and common marketplace for NFTs and if you're looking for a "different" way then you can just go back to the usual method of selling it through P2P but this is a harder way. It's like selling directly to those people that have the same interest as you with the NFT that you're trying to sell.

I'll give you an hint. A simple rock NFT was sold for $1.7M.