I think you misread GP, they only said the appendix is not an evolutionary mystery, not that it doesn't serve a purpose. In fact, he noted the presence of lymphoid tissue, which makes is useful to the organism, as stated by the article as well.
I don't think I misread GP:
"they're just the ends of things that come together."
[something about cyclops and male pregnancy]
"Fun stories, completely useless"
Exactly. Sort of like getting a picture and the metadata says "Nikon". Probably that picture didn't come from midjourney.
Note, GP explicitly mentions the following in their last paragraph, and make no claims that the appendix is useless:
> This idea that the vermiform appendix is some deep evolutionary mystery is sort of a low point of medicine that occasionally pokes its head up. It ranks up there with male pregnancy, and various birth defects that have given rise to stories of monsters, like Cyclops. Fun stories, completely useless.