Hello and welcome to OKP, shadowy demony person.
As others have said, "demon" is a very wide term that can be used for anything from a non-corporeal scary entity, to a being from Christian mythology (or rather, from the pop culture version of that mythology), to assorted scary-looking creatures from other paradigms, to any creature that looks big and has horns . . . and there's no reason why any of those entities would be related to one another. So, like others in this thread, I don't much like to use it.
"Shadow" is a relatively new term. It's been used in the context of dark energy being for maybe 10 years, "shadow person" probably longer, but again without a whole lot of variations. I have no attachment to the term so I'm happy for alternatives - another OKPer has used "skianthrope" (which means shadow-person in the same way as lycanthrope means wolf-person, I think) which I also like a lot.
Anyway, from your description, if you were asking what I thought you were, I'd vote for probably shadow. Dissociation (feeling like your life is a movie you're watching, rather than reality) is fairly common in non-physical otherkin (energy beings and the like). A definite humanoid body with extra appendages (in your case shoulder spikes/stubs, in my case spines and tail) is very common with shadows. (Why is a whole other question!) Interestingly, while there are some shadows who take the shape of a sort of vague nebulous cloud, and some shadows who have very "solid" forms, there seem to be very few who shapeshift or drift from one form to another. (Again, I could speculate wildly about why this is so.)
I'm sensing a bit of ego in you too <!-- s

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--> This is all circumstantial evidence but in my experience shadows are rather prone to thinking we're big cheeses, not to be messed with, etc. The sensation of getting a glimpse of an image, and not fully understanding it, but feeling rather ancient when it "connects" is also something that seems to happen more with energy-beings than other types of people.
Note, I'm not saying "OHMYGOD UR A SHADOW!!!!" But, I generally define "shadow" as a non-physical energy being made of a kind of dark energy that some people might find difficult to identify and the majority of non-shadows find scary/intimidating. Which seems close to how you describe yourself.
You said you can communicate with "goetics" - I'm not familiar with the term, what are they? I'm also very interested in the things you're feeling near your shoulders. Can you describe more about their shape or how they feel?