Operating system: Windows10
Graphics card:Geforce GTX 970M
Short description of error
When you load an Image/Texture with an alpha channel in the UV editor, you can't turn the alpha channel off anymore, the image will stay black.
It worked in older Versions from 2.80 up to 2.83, there you only have to click on Color in Display Channel options.
Only areas that aren't black in the Alphachannel will be visible, in my examples I work with textures that need an all black Alpha channel.
Exact steps for others to reproduce the error
just load any Texture with Alpha channel in UV editor viewport
Here an Screenshot from Blender 2.83.0 where it worked
and here an screenshot of Blender 2.91.0, the same Texture is used, I also tried different settings under Image, but nothing works