Hello. I think it is a matter of defining the term 'being'. If being is defined as "a thing that exists", then a "non-existing being" is a self-contradiction. If on the other hand being is defined as "a thing that is a unity or individual", then a "non-existing being" is possible. I am leaning towards the latter definition, because I have heard other people talk about "imaginary beings" like unicorns. That said, I don't think that contradictions can be beings, like "a thing that is both a unicorn and not a unicorn".

It's reasonable to say that any self-consistent possible world, and anything in it, exists.

Likewise mathematical theorems, abstract logical facts, etc

I think that the word "actual" (for us) is usually reserved for what's in our own physical universe.

Michael Ossipoff

Are things that are impossible — gunner

What do you count as impossible?

~E!(the x: Fx & ~Fx).