Make a new layer. Move it to the bottom or at least under the layer you made 50% opacity. Fill that with white.
Is that what you expect ? Export that as a png and the layers are merged.
Edit: Just wondering what you intend to with the 50% opacity image. Is it to add over some other image ? Maybe you should keep it with the alpha as-is. The checker pattern only exists inside Gimp (or some image viewers) as an indicator. It is not real.
Is that what you expect ? Export that as a png and the layers are merged.
Edit: Just wondering what you intend to with the 50% opacity image. Is it to add over some other image ? Maybe you should keep it with the alpha as-is. The checker pattern only exists inside Gimp (or some image viewers) as an indicator. It is not real.