Tutorial for making PPSSPP PawaPota texture dumps not transparent:

This tutorial applies to the PawaPota games for PSP, but it may apply to other games that handles textures like this. I'll be using this sprite dumped from PawaPota 3 as an example.

Open the texture In Photopea (this probably works in Photoshop too).

Go to Layer > Raster Mask > From Transparency.

Click on the newly created Raster Mask (The little black and white thumbnail).

Go to Image > Adjustments > Invert or press Ctrl + I.

The sprite(s) should show up now.

Unfortunately, I have not found a way to do this in bulk, so you'll have to manually repeat the above steps for each texture.