Why is everyone focused on the umlaut? If you don’t have the button, use a “u” and move on.

That's not a keyboard issue. Everyone in my country uses a standard US keyboard, we just press AlgGr to type some characters. I even learned some foreign lanugages, so I use a (standard, included by default in every linux distro) keyboard layout that allows me to type most characters used in European languages by using chords - for example, alt-shift-2 + u = ü.

So this is not a keyboard (hardware) problem, just a keyboard layout (software) problem.