I was asked when to use beide and when to use beides as well as alle vs. alles.
Here are two examples:
Tee oder Kaffee? Ich mag beide Getränke. Egal, ich trinke beides.
Ich habe alle Übungen gemacht. Ich habe alles gemacht.
I think the reason is that in the first example the words are adjectives and in the second sentence they are adverbs, but I’m not sure.