I don’t blame anyone for not knowing that ü = ue if they don’t speak German, but if you are/were one of those people who didn’t know this and just ignored the umlauts altogether (Hügelkultur -> Hugelkultur): the ü and u, ä and a, ö and o... are all different letters. They are not simply modifications to the letters a, o, and u. They are different letters entirely, which can also be represented as ae, oe, and ue. But they are NOT the letters ae, oe, ue, if that makes sense.