In my view abstraction has to come well before consciousness, so I think it should be able to exist outside of some entity with consciousness.
Living beings for instance seem to me to need to "define" the world and maintain physical boundaries with it to exist and perpetuate themselves.
I don't think there are any objective abstractions though, boundaries and definitions are built and maintained by subjective entities, their maintenance of a separation of sorts, and their interaction with the rest of the universe.
Yes, usually some wide variety of various types and instances of abstractions are only relative to a culture or condition...
But not all are relative (I think).
One way to think about number as being some absolute basic thing in itself (just a wording), that is, independent of all entities or conditions, is whether totally unalike civilizations or intelligences would discover (find) it, on their own, and it would be the same thing. It's generally thought yes -- number would be, even math generally would be, as "universal language". But I only point to that being a common idea just to suggest it's worth considering. To me, it seems evidently so, though. Number -- 1, 2, 3, 4, 5, 6 (regardless of base, so, 1, 10, 11, 100, 101, 110, etc. (base 2 if I remembered it the right way) is identically the same, in essence -- the universal language being number itself, and more generally, math). It would not matter where or how the intelligence exists, it would in some sense discover this absolute thing, this fundamental...thing, that exists outside of any constraints of any kind.