I had der Bär! Typical Duo.

Lol

Yes, Vogel here is in the accusative.

I think it's because of acusative. I'm not sure tho

Vogel is masculine, and it's in the accusative, so it changes to den. :)

I have the same Q

Press-Hold the "s". Beta is almost equivalent to double-s, so normally it is there (tested on Xperia Z and Samsung)

Try to push the letter S for a second, it is usually under that sign.

German Eszett is ß, while Greek Beta is β. Their glyphs may look superficially similar but they are not the same letter. German Eszett does not have a tail and does not have an uppercase form and it originates as the merging of the letters ſ (long s) and ʒ (tailed z), representing the sound for "voiceless alveolar fricative" (the "s" sound). Greek Beta is the lowercase form of the letter B, representing the sound for "voiced bilabial plosive" (the "b" sound) or the "voiced labiodental fricative" (the "v" sound).

Change the dictionary of your keyboard (of your cellphone) to Deutsch and then keep 's' button pressed and the symbol should appear. :)

Opa ist ein Spitzname für Großvater. Meine beste Vermutung ist, Duo will man es buchstäblich zu bekommen richtig. Opa is a nickname for Grandfather. My best guess is Duo wants you to get it literally correct and know the correct term.

Man würde ''Fressen'' mit Tiere benutzen, zum Beispiel:
• Der Hund frisst das Fleisch.
• Die Pferde fressen Äpfel.
Auf der anderen Seite, würde man ''Essen'' benutzen wenn man über Menschen spricht, zum Beispiel:
• Der Arzt isst keinen Apfel.
• Die Eltern essen keine Orangen.
Ich hoffe diese Erklärung hilft...