The problem with Art is Art is whatever the Artist says it is. There is no concrete definition of Art, it is wholy subjective to the perspectives of the creator and the appreciator. Comics & Manga certainly fall under the umbrella of art in a strict sense, they are first and foremost Comics & Manga.

Colloquially when people say Art they mean what they see in a museum, not what they can buy in the corner store. When I subscribe to a generic Art category I want to see artists showing techniques, cool paintings, breakdowns of how marble was carved, and most certainly not catgirl uwu. I might be interested in a post about how comics are made (high effort, interesting content), but I am not interested in a picture from issue #346 (low effort fandom attraction).