como manter a opacidade ao salvar ou Mesclar as camadas

I’m trying to make a tileset for a game but my arts usually have many layers with different opacities and modes, but when trying to flatten/merge the art or even export it as an image, the opacity layer doesn’t stay.

use english on your title please(eu falo portugues tbm mais ingles e a regra do forum), are you using png? also are there color below the opacity ones, if so when flattened they will become a single color, that how flattening works.