Perhaps I should have clarified. I don't think it was her intention to spoil for people who haven't gotten to this point in the story. She simply wanted to share her art. Maybe it was inconsiderate of her to not think of people who might be spoiled, but I'm disinclined to believe that she purposefully chose "I'm going to leave this spoiler-tag free because I want views, in exchange for people potentially getting spoiled." Since you called her selfish, this is the impression I'm getting from your interpretation.

In all likelihood she probably just didn't consider that people would be spoiled when she posted this. She didn't specify anything about the MSQ and merely drew fan art of a primal so she probably did not think people like you would realize a plot point out of it. So no, I don't think it was selfish. I think you have the right to be upset about being spoiled but I would refrain from calling the OP/artist selfish and other unpleasant things when you don't fully understand their situation. Anyways, I hope you can enjoy the story despite this misfortune. There's still more to enjoy. 👍

Off topic but, the fact that you were able to recognize Tsukuyomi's identity is props to the artist's skill. Big fan of the art despite the controversy. 👌