You do still need to select compression of BC1/DXT1 and tick the box to generate mipmaps - both in the the dialog box that pops up after you select export image and set the directory/filename (with .dds extension).
You do still need to select compression of BC1/DXT1 and tick the box to generate mipmaps - both in the the dialog box that pops up after you select export image and set the directory/filename (with .dds extension).