This is advance fee fraud. The scam is they pocket the "gas fee" and disappear.
anyone who's offering you money, but then telling you you have to pay a fee to get that money is a scammer, whether that's a supposed nigerian prince with his money in a foreign bank, a "world lottery", or someone trying to "buy your art"
an honest NFTbro would have paid the gas fee/taken it out of the offered price of the artwork.
I knew this was the case when the "buyer" approached me and went along for a giggle to see how long it would last until the scam is revealed.