The cause of the universe must itself be uncaused, or else it is only an intermediate cause that must itself refer ultimately to an uncaused cause. An infinite regress is impossible with respect to existence. Unlike causes per accidens which can in principle be infinite in length, a cause `per se` cannot; without a terminus, there would be nowhere from which the latter causes would derive their force, so to speak, like an arm pushing a stick that is pushing a rock that is pushing a leaf. Meaning, the cause is not some distant one in time, but one always acting; otherwise, everything would vanish. The only cause that could have this property is self-subsisting being.
From there, you can know quite a bit about what else must be true of self-subsisting being.
There doesn’t need to be a why the world exists. It does that’s all there is to know. There doesn’t have to be purpose just an explanation of how not why
Sure but that's somewhat tautological and not very helpful if you seek an empirical or predictive understanding of it. The question really is what complexity of the system (meaning: all of it) is irreducible and what can at least be approximated with simplified models.
You may balk at this as being ultimately futile but our entire existence is built on trying to break apart and simplify the world we exist in, starting with the first cut between self/inside and other/outside (i.e. "this is me" vs "this is where I am" - a distinction that becomes immensely relevant after the moment of birth). Language itself only functions because we can create categories it can operate on - regardless of whether those categories consistenly map to reality itself.
