that’s because they are, umlauts came from writing vowel digraphs as the first letter with the second letter above it, for example ueber/veber -> uͤber/vͤber -> über/v̈ber -> über (although über in particular didn’t actually originally have the spelling ueber). “e” turned into two lines, which now is represented as two dots/a diaeresis on most computer fonts. that’s why, if you don’t have access to diacritics (e.g. on technology), you write ä/ö/ü like ae/oe/ue (and why you have names which are spelled like Goethe instead of Göthe)