Here is a link to an article and video about Kurt Vonnegut’s masters thesis on “story shapes”. While not specifically about comics, it applies to all stories in any medium. Personally, I find it more specific and helpful than the traditional Fretag triangle, and—at the very least-it will give you a new perspective on plot and storytelling.
Also, if you’re new to Vonnegut, watch the video. The man is (was, today is the anniversary of his death) hilarious.