Can you see what's wrong?

Absorb doesnt work on group attacks huh?

Group attacks counter the move absorb. It attacks all compys or flock creatures at once.

But it didnt “bypass” absorb

Hmm I just checked and it looks like acro’s move GCS doesn’t target all opponents. For some reason

It’s because Group Cleansing Strike doesn’t target the opponent’s group, it targets yours. This is more of a Raid ability, so if you go into a raid and use it, you’ll see that the real effect is that it cleanses your whole team from all negative effects.