Special characters keyboard/German Umlaut ä, ö and ü

Hi Apple Community! I am using MacOs Catalina on my MacBook. I write German content on an American keyboard and used to just hold the vowel button and it would give me the option of various variations of the vowel including the "Umlaut" ä, ö and ü. Now when I hold the vowel button, it just keeps entering it like any other letter (like this: oooooooooooooooooooooooo). Does anyone have an idea how I can reverse this and get back to the old hold the button feature?

Thanks in advance!