What "an observer" really means, in the context of QM, is a large, approximately classical system interacting weakly with the system being "observed" (such that

What "an observer" really means, in the context of QM, is a large, approximately classical system interacting weakly with the system being "observed" (such that the interaction can be modeled perturbatively). Humans "observe" photons, but so does a pail of water. It's a way of framing certain classes of problems, not a distinct sort of entity.