It is really no longer necessary to use ALT codes when trying to type in German on a US Keyboard.
Under Windows, which it sounds like the OP is using, it is possible to switch to the US-International Keyboard layout.
Here is an Internet resource on how to do it: https://resources.german.lsa.umich.edu/schrei...
To type umlaute using the US International Keyboard layout, type a quotation mark (") and then the letter over which you would like the umlaut to appear, i.e. a, A, o, O, u, or U. Nothing will appear on your screen when you type the quotation mark; once you type the a, o or u, the umlauted ä, ö or ü will appear. Note that when you actually want to type a quotation mark, you have to type the quotation mark followed by the space bar to make it appear.
Use the RAlt key (or Ctrl + Alt) to type ß: RAlt + s = ß
It can also be used for typing in other languages, such as Spanish and French.
This is a much more elegant solution than having to remember and use Alt codes.
One can also switch between whatever "normal" keyboard was in use and US-International by selecting between the two layouts on the Windows language bar in the task tray.
Give it a try and see if you like it.
Here is an additional resource that shows the different key combinations for different characters: https://dry.sailingissues.com/us-internationa...