I think it is this bug GIMP DDS RGBA output has full-white alpha channel see: https://gitlab.gnome.org/GNOME/gimp/-/issues/6215 White alpha channel = that totally black image. Who knows when that will be fixed, although there is a suggested work-around.
Alternative: Not Gimp, since you are a Windows user try paint-dot-net AFAIK it has a dds plugin.
edit: A bit of searching
If you feel like command line http://www.imagemagick.org use then this certainly produces a .dds file equivalent to a png with transparency.
Attached that .dds. Can you try it in your dds viewer (I use linux and the only viewer I have is XnViewMP)
Alternative: Not Gimp, since you are a Windows user try paint-dot-net AFAIK it has a dds plugin.
edit: A bit of searching
If you feel like command line http://www.imagemagick.org use then this certainly produces a .dds file equivalent to a png with transparency.Code:
magick test.png -define dd:mipmaps=1 -define dds:compression=dtx5 'DDS:test.dds'Attached that .dds. Can you try it in your dds viewer (I use linux and the only viewer I have is XnViewMP)