They are cheap and if you don't need an expensive product, they are mostly fine, but I got a free powerbank with some crappy teen magazine (when I still ocasionaly read those ad filled pieces of shit) and it died on the second charge.
Assuming it was either 15 years ago or your powerbank is a budget one.
My powerbank would just flip me off and tell me to go fuck myself if I did plug it into itself.
(seriously tho, it would just cut power and turn off immediately. If your powerbank doesn't do at least that, then discard it and get another one with more advanced protection features)
And it was probably cheap Anker instead of expensive Anker? Maybe that shit just hadn’t hit consumer products yet as well. But yeah, Anker offers a HUGE selection of products from consumer to professional.