Logo with opaque background:

Taskbar icon with opaque background:

Logo with transparent background:

Taskbar icon with transparent background:

i got this strange rendering in 1.14.4-1.19.11 thanks to this information, I will now add a transparent layer that won't be visible but I think will solve the issue.

Yes that worked! I used GIMP to add a transparency layer to my icons. I use all the space on a set of icons in some instances. Simply adding the transparency to the image and that was enough to make it no longer scrambled.

Almost a year late, it turns out I just needed to specify four channels.