This is too pessimistic. We can absolutely "begin to guess" at what an alien civilization might look like or how they might have evolved. Reasonable possibilities are very heavily constrained by information theory, the laws of thermodynamics, the very finite number of elements that make up the universe, chemistry, particle physics, etc. You can appeal to fantasy by dreaming up multi-dimensional energy beings, and of course such things have some tiny but nonzero probability of existing. But you can do the same thing regarding what we might find if we look at some random pond water under a microscope. Maybe we'll find crazy silicon-based life forms, or some phylum we never knew existed, or a microscopic Tyrannosaurus Rex! Maybe. But it's perfectly reasonable to ascribe an extremely small probability to such things based on everything we already know about the universe, and it's reasonable for the same reason to ascribe a very small probability to the existence multi-dimensional energy beings that would completely defy our understanding. For any given alien life form we might find, there's a very high probability (I give it at least 90%) that it would be based on chemical pathways that would make us go "oh, neat", but not go "THIS CHANGES EVERYTHING!"

I'm a complete layman, but I wonder if chemistry on Earth (and rest of our solar system) is also influenced somewhat by the particular properties of our star, its and our magnetospheres etc. and the gas clouds our planets coalesced from.

As in, different stars may encourage slightly different chemical reactions and interactions on their planets.

Like, for example, could it be possible for a planet to form with a naturally highly magnetized mineral in its crust? Would it affect the rest of the chemistry on the planet? Would it cause the ground to interact with its star's magnetic envelope, like our atmosphere within the Auroras does?