URP Lit material has a slightly white Background

Question

i'm having trouble with a simple Lit URP Material. It always exhibits a slightly white background, no matter what PNG i use. Here is what it look like:

screenshot

As you can see, the background is not completely transparent.

These are the Material settings:

material settings

And here's the PNG import settings:

imoport settings

Is this expected behaviour? How can i avoid this background issue on a Lit Transparent Material?

Any hint is welcome!

I want to create a Lit Smoke Particle system. It should work with a Lit Material which should have a compleletely Transparent background.