Odd dark nebula structure.
Least that is what I assume it is. Really stands out, almost 3d. Looks like it might be a small dark nebula that is very opaque with foreground stars that almost give it a 3d quality.
I commented elsewhere that I see 2 kinds of dark nebulae -- one we see as concealing and essentially flat, but the other seems to be spheres or oblate spheroids (doorknob shapes) that appear to affect the star material around them -- exclude it from where they are -- so they get circled by stars, clouds go around them not through them, and so forth. I can't tell from the object alone which area you were talking about, but the upper left corner looks like a crowd of those lumpy ones. I use the marking tool (square/rectangle) which, when I put it over an area of them, makes them stand out from the cloudy surround.
Seems like the obscuring, flat nebulae show up almost shiny, while the lumpy ones are matte.