How to type ß (Eszett) on Mac OS

How to type this ß (Eszett) or weird-looking "B" as I knew it before in Mac and iPhone.

Mac OS

The "s" needs to be lowercase.

alt/option/⌥ + s

iOS

Using the German Keyboard: here is how to add new keyboards.

hold down "s" and choose it from the list

This is how it's going to look if you hold down the key on a uppercase "S".

Here is if you hold down lowercase "s".

Why is this weird-looking "B" under "s" instead of "B", well in fact it is because is an actual "long s" sound, also called sharp s.

What am I doing with this?

I started to seriously learn German, well, using Duolingo, Duolingo-serious, and while I have been using the app it never gave me a wrong answer using "u" instead of "ü" or "b/B" instead of "ß", but it started to giving me this as a wrong answer.

Notice the lowercase "s" in Schokolade.