Logical positivism

Have a good week!
1- If I understand correctly (?), logical empiricism adds to the words of Hume and Locke that not only are the concepts of thought constructed by observation and are not innate a priori in man, and in any case Hume claimed that we have never encountered concepts such as “infinity,” “causality,” “God,” etc., but that metaphysics has no cognitive meaning at all and these concepts are nonsense.
That is, while today they have no objective value and do not exist in reality, the Viennese Circle adds that they mean nothing to man either?
2- I don’t understand where their assumption comes from that a concept whose word does not point to an observable signified has no meaning (and is like a private language). Maybe they are right that concepts that are not empirically tested do not exist, but why shouldn’t they have cognitive content?
3- According to the positivists, it follows that a scientific theory cannot describe theoretical entities that are not observed, and as Mach (the father of the positivists) did indeed state, a scientific theory never assumes that there are objective entities, but is merely a convenient and practical way of relating to reality, but every case in nature is nothing more than a private case.
And so, K. Lee, how can we even talk about, for example, the principle of causality that is not observed, and indeed, Yom claimed that it does not reflect reality but rather the person, but according to Carnap, would we have to say that causality is nonsense?
In other words, how can Mach claim that theories are just a convenient way, and it turns out that there is no point in talking about it at all, and what nonsense, and how can we even refer to it if it does not reflect reality itself?
4- How can one, according to them, speak of concepts such as “ownership,” or even how can one refer to a group of items as one, and yet the way to relate items such as a triangle to each other and define them as a triangle is either through Plato, who sees the idea of ​​the triangle, or through Aristotle, who claims that it is only an abstraction made in thinking. And so how can one refer to the generalization of things, and yet the very generalization is not empirically observable but rather personal (according to Aristotle and certainly Plato), and therefore cannot be pointed to?
How can psychological theories and even any social situation be described, let alone the very general definition thereof?
5- Mainly, why do they claim that there is more cognitive value for scientific phenomena, even though they are just a convenient way to relate to reality and are not observable, than for God. And since it is possible to relate to and use the principle of causality, etc., even though they are not observable, and for the sake of convenience, we can relate to and use and talk about God (even though he does not necessarily exist and is observable, as in a calculation), since the concept of God is a convenient way to build a theory about the world since it explains its existence, and since the principle of causality is not nonsense, even though, according to them, it does not exist, and therefore this concept can be used?
6- How does science work, according to them? What do they mean by a particular case and not by truly seeing the real? How do they simulate phenomena and construct a general law?
Thank you very much!