On a similar note: my iPhone very often autocorrects wurde to würde and hatte to hätte when typing German. These are all extremely common words (and part of the built-in dictionary). The one it "corrects" into are even less common. As the keys are on opposite ends of the keyboard you can't mistype that. Very annoying.
If someone knows how to disable that without switching off autocorrect altogether, I would be very glad to know.
i just long-press the letters if i really need an Umlaut, but generally i just type the normal one and use the suggestions to switch to the correct spelling.
Autocorrection is dependent on your keyboard btw. It might be a good idea to try a different ones. I haven't really had that issue since i've switched to GBoard, but i remember struggling with the same problem before as well.
However, the virtual keyboard I'm currently writing ^W swiping this on does not have dedicated keys for them. I have to long-press [a] to get a popup with variants, including [ä].
The dedicated äöü keys were added in some update a few years ago (there is no ß key). At that time you could only get German autocorrect with that keyboard (I think) so I got used to it. At some later point they added autocorrect for all other installed languages to that keyboard so I now use it exclusively (due to the extra keys they differ in width between keyboards which is confusing when switching).
If someone knows how to disable that without switching off autocorrect altogether, I would be very glad to know.