Thank you for asking and the responses. It would have helped if Duolingo provided help tips that certain words are different for men and women.
Why not arabiyyah?
3arabiyyah is female, 3arabiyy is male. You will see this with a lot of adjectives and nouns.
because "arabiyyah" is feminine
It is the same.
We add (ة) to the singular feminine in adjectives only, for example, she is beautiful هي جميلة, she is smartهي ذكية، but in the masculine singular we do not add (ة).
Where are you from?