In the Copenhagen interpretation we may not ask in what state a system is in until we measure it. I.g the double slit experiment we can’t say that the particle went through both slits, we may actually not say anything about the particle(except that it behaves like a wave) since we haven’t measured it and therefore it isn’t in any specific state yet. Or that a particle has a specific spin until measured
The interpretation says that the wave function isn’t a real thing; it isn’t the particle itself. This means that half of the particle doesn’t go through one slit and half of it through another.
One thing with the Copenhagen interpretation which has been criticized is that it doesn’t specify when a measurement is made or more commonly said: when the wave function collapse happen. This means that in the interpretation it doesn’t say whether a particle takes on a specific property when the measurement occur or when someone looks at the measured particle or anywhere in between.
This has lead to the myth that the Copenhagen interpretation should treat consciousness different from something non-living. That is wrong Copenhagen doesn’t need consciousness to work. The reason it doesn’t specify it is because to honor the famous/infamous the-devil-may-care attitude of the Copenhagen interpretation, when the collapse occur doesn’t affect anything, we can’t see any difference in the real world and therefore isn’t a sensible question. It can still be considered unsettling(in fact the entire interpretation can be found unsettling) The instantaneous collapse leads to non-locality.