Layer Export Issues

So I made a sprite and decided to add a layer on top with the lighten modifier with 80 opacity.
Trying to export the sprite as a png only exports the lighten layer with 100 opacity.

Trying to merge the layers deletes the opacity of the lighten modifier and ends up with the same result…

I think I found a way to apply the lighten modifier layer to the export. I had to switch the colour mode of the sprite to RGB from index’d and create a new colour palette. Worked fine after that.