If someone could spare a minute, is this unburnt gunpowder or is something going really wrong with my new AR?

Yes, that's unburnt powder.

What's your barrel length? Do you use a suppressor? What type of ammo?

Things that can contribute to this include:
-Barrel shorter than 16ish inches (most common)
-Subsonic ammo
-Backpressure from suppressor
-Overgassed
-Cheap ammo or reloads with powder that's too slow-burning

A quick perusal of your prior posts suggests it could be a combination of all/most of the above factors.

Sounds like this is your new SBR that you just assembled, which you likely were shooting with one of your suppressors and some of your .223 handloads?

If so, you're definitely going to be getting unburnt powder blowing back into the receiver.

You can try tweaking your load with a faster burning powder to help reduce it.

You’re correct on most of it (your cop skills are getting rusty)

The gun is in fact the freshly built SBR with a 10.3” 300 Blackout barrel. The gas duties are being handled by a Superlative Arms adjustable gas block. Due to other main goals for yesterdays range trip I literally only shot 3 rounds. The first was at arms length unsuppressed as a “It’s my first upper build, if it blows up I want it to be at arms length.” shot. It didn’t cycle at all. Shot 2 was with a suppressor and it extracted the round but didn’t fully eject it and the third round did the same as the second so back to the case the gun went and we shot other guns.

I have noticed that the bolt carrier is tougher than my other ARs to cycle so there is that tidbit.

The ammo I question for the day was Hornady’s Black line of 208gr subsonic ammo. I probably should have started the show with supersonic rounds to break stuff in but I really wanted to see how it sounded suppressed with subsonic rounds.