So no matter what I try I cannot get it to save in a compatible format.
I’ve read all I can find on the matter and tried every suggested export setting.
I’m using photoshop with the nvidia plugin I’ve tried dxt1,3,5 18.104.22.168 I just cannot work it out.
This answer might come far too late for your liking, but I hope I can help anyway.
I had the exact same problem, with both GIMP and Photoshop. I ended up downloading PAINT.NET, which has native DDS capabilities. I start by loading up a random dds file from the game, erase everything in the image, and draw what I need. It works perfectly for me.