Context
We have to find the artist’ address Ethereum.
Resolution
I used OpenSea website to find the artwork.
I searched for “blanc avec des liserés blancs transversaux” that seems to be the name of the NFT bought.
These are the first results:
The single color NFTs belongs are owned by Antrios who the artist mentionned in the initial statement.
On his profile, we get his Ethereum address.
The flag is 404CTF{0xD7186D588Ed2AddF8b260d09B108100f264A64A9}