also…please check well that your image is in RGB mode (go to top menu, ensure is not greyscale or indexed) …(in same menu, is ok if is set as 8bits (that means not it is as indexed…is 8bits/channel))
Also, the alpha in the way you seem to be making, is not usually how it’s made…You’re making a layer mask, and can’t check right now, but I think tga exporter wont take that…Instead (similar to how done in gimp) you can simply “select” menu at the top, and save your selection. That is: new channel. Or go to the channels menu and generate a new channel, but for me save selection is faster an cleaner.
Now once you export the tga, two new things will appear, the checkbox of Alpha marked and not grayed out, and once you hit save, a little popup with the tga options, which surely didnt trigger before. Please, set there “32 bits”, or it will definitely not save the alpha channel.
Anyway, yep, I also prefer PNG, but u can use perfectly TGAs with both Gimp and Photoshop with alpha channels.