"unlockables" is a feature in nfts. only the owner can see the unlockables. no one else. it can be an image or text. I did one with higher resolution, higher quality image on for the buyer to see or download. the public only see the low res art. I did one with a text. links to how to paint with a lot of images.

unlockables are great. nfts can be used as tickets or access to a party. A club thing. Only people who owns my paintings can get into my party with nft. you can swap it for something. else. GaryVee explains it well, https://www.youtube.com/channel/UCctXZhXmG-kf3tlIXgVZUlw