As the Wikipedia article on the observer in quantum physics puts it:
"The prominence of seemingly subjective or anthropocentric ideas like
'observer' in the early development of the theory has been a
continuing source of disquiet and philosophical dispute."
The Copenhagen Interpretation fudges the issue, by keeping a classical world, and having a quantum world only below the decoherence limit, bridged by observations. But why is the coherence limit where it is? Why does classical behaviour emerge, if everything is, fundamentally quantum stuff?
The scope for speculation about the quantum measurement to get even very great minds coming out with daft ideas, like the Wigner-Vonneumann Interpretation, has led to a lot of institutional hostility in academia towards funding work on foundations of quantum mechanics. That is starting to change because of the obvious need for more radical thinking in order to integrate gravity with the quantum picture, though it is difficult still to work on for academics without tenure. Given the different interpretations will likely remain unfalsifiable, there is a widespread feeling among professional physicists that it's not an area of physics, but of philosophy.
From the Wikipedia page on the Uncertainty Principle:
"Historically, the uncertainty principle has been confused with a
related effect in physics, called the observer effect, which notes
that measurements of certain systems cannot be made without affecting
the system, that is, without changing something in a system.
Heisenberg utilized such an observer effect at the quantum level as a
physical 'explanation' of quantum uncertainty. It has since become
clearer, however, that the uncertainty principle is inherent in the
properties of all wave-like systems, and that it arises in quantum
mechanics simply due to the matter-wave nature of all quantum
An exact quantum measurement would intrinsically increase uncertainty in conjugate variables, so knowing speed totally would wipe out knowledge of position, etc.
I like Aaron O'Conell's Visible Quantum Object experiment. Information about quantised changes being either isolated or transmitted and so spreading out, seems to be one way of picturing things.
Chiribella's Purification Principle seems to be a workable way of picturing quantum measurements as the spreading out of correlations, the diffusion of information about past states of particles. Pure states becoming mixed states.
Basically an observation joins a system we call quantum with one we call classical, into a new system we call classical. This is unsatisfying philosophically, but the sense that it wasn't getting in the way of experiments made it a low priority for half a century. Developing a picture that explains observers and the quantum coherence limit and the emergence of classical from quantum behaviour is a set of open problems, which issues like entanglement have underlined the need for.
I wouldn't describe the separation of observer and observed systems as dogma, but as idealisation, like the idea of a thermodynamically closed system. Neglecting interactions in both cases makes calculations tractable, but at very small scales becomes an issue. Maxwell's Demon helped us understand the physical reality of information in relation to entropy. Uniting quantum fields & general relativity looks to involve close scrutiny of rest-frames & information flow.