(If you can't tell, I fully subscribe to the Many World interpretation. AFAICT it's, by quite a long way, the most parsimonious explanation in terms of extra "theoretical stuff", even if it is "wasteful" in terms of the amount of actual stuff it posits.)
MWI just posits that the measurement apparatus exists in a single world, while the particles exist in many worlds. But it can't explain this basic fact, like any other interpretation. What we need is an actual new theory that can actually measure what a measurement is (at what precise point the Born rule must be applied, or how can we do without the Born rule).
Their are some hidden variables which means it’s deterministic and there is no amplitudes involved. The universe has some sort of random number generator which determines the outcome. They don’t actually collapse, which is what the many worlds theory essentially posits.
That's not consistent with classical physics, and it is not what MWI actually posits. The universe branching that MWI posits is not really different from wave function collapse, and decoherence also doesn't really solve things. You still fundamentally have a single position for any classical system, but multiple positions with different amplitudes for quantum systems, and some mysterious threshold where you pass from one to the other.
Probability also can't really explain this, since the classical model also applies to single particles after they have interacted with a macroscopic system.
MWI considers that observers inside one branch can't interact or notice observers inside other branches, and this is why we perceive the world as if objects have unique definite positions. But this still doesn't hold up for quantum systems, which do in fact perceive and can interact with all of the other "worlds", including interacting with themselves in other worlds such as in the single particle double-slit experiment. So MWI doesn't really get away from the duality in any rigorous way.
You can’t experimentally differentiate between MWI and single universe wave function collapse.
Apparently this has become easier to swallow after all the research that has gone into QM during the past century.
There is another interpretation that can also be considered as close as possible to no-added sugars, the "ensemble interpretation". In "ensemble interpretation" the formulation of QM is understood to be applicable to ensembles of similarly prepared systems. In this interpretation QM is not really applicable to a single system by construction.
In MWI you accept it can be applied to a single system but you have to pay as a price that the system can branch into many different ones simultaneously (the "many worlds").
It's a kind of pick your own poison situation.
"Consciousness"/"Observer" etc are too high level concepts to matter there.
I don't need to choose the experiment directly, I can make a complicated arrangement that then picks the experiment to be executed. (Let's say, I make a random number based on the current wind speed and I make a mechanical apparatus that throws a die and choose the experiment based on that). Try changing that experimental freedom.