Wait I assumed that NFT marketplaces like OpenSea stored a hash of the artwork in the layer 1 blockchain. Please someone tell me this is actually happening?!
It's usually a URL of the artwork that is stored on the blockchain.
That URL is sometimes an IPFS url, which is a hash of the content. But it could be anything, that's why you can create NFTs which change their image based on where they are viewed, or eventually 404.
3rd party wallets often don't bother looking up the blockchain to find the URL. They just query a centralised API like the one run by OpenSea. That's why OpenSea blocking an NFT can make it show up as blank in 3rd party wallets.
