I did check of transparency of PNG images in blender 2.81 (linux version).
I found this minor bug. It only occurs when using mtpaint. KRITA images worked fine,
as shown in image below. Also I should mention that cycles rendering showed the transparency fine. No problems there!!!
Here is how to reproduce the problem...
- new gimp document -no alpha channel - paint with brush
- save as PNG format with no alpha channel
- mtpaint ---> open the PNG document
- save the document - one color chosen to be transparent - PNG format
- blender - images > Images as planes
EEVEE rendering doesn't respect the transparent region.
Cycles rendering does respect the transparent region.
I did the same procedure with KRITA substituting for mtpaint and there was no problem.