When people (typically scholars) work to put Genesis 1 into some sort of non-realist box, they, at the same time, express a view that Genesis 1 is not the foundational definition of all that is, of our relationship with God and the real world he created, but relies on some other, unstated foundation.
Thus they have Genesis 1's teaching in some sort of idealist bubble in a world that has its foundational being, its cause and 'creation' from some other source. This world is not really aligned with God, but God and his creative works become clients of this other world that is definitively foundational and inevitably reflects the terms of its foundation.
Typically this foundational definition is, today, what I would call 'ethical materialism', or ontological 'naturalism'. Where what really is is random uncalibrated and morally nebulous interactions of molecular assemblages. This world is not morally deep, but mechanistically shallow and personhood is an accident within this world, not foundationally prior to it.
