Aristotle's unmoved mover argument (and it's slight variation in Aquinas' cosmological argument, and the whole class of arguments for the existence of God of similar general form) are discredited in the sense that they either (1) rely on equivocation, or (2) are internally inconsistent, or (3) simply introduce an additional unproven entity without explaining anything, or (4) even if one assumes it's completely true, it doesn't prove the existence of anything like the usual conception of a personal God anyhow. (The options aren't mutually exclusive, though usually onky one of the first two applies, depending on exact definitions of terms—though often those definitions are unclear enough to be uncertain which of the two applies to a particular argument.)
If "everything in existence depends on something else" is a valid generalization, introducing an entity with out such dependencies is a cobtradiction.
OTOH, if it's not a valid generalization, any number of things in existence could lack such a dependency, and there is no need to assume a unique and special unobserved entity with no dependencies.
An independent common first cause or unmoved mover is, perhaps, an aesthetically pleasing (for some) solution to the apparent problem that things generally seem to have causes but infinite regress is an unappealing belief. But it is neither logically necessary, nor does any first cause necessary resemble God (the Big Bang works fine as an uncaused cause on which all other events in the universe depends, and isn't anything like any traditional concept of God, as, more generally, does any initial state inferred from modern observations of physics.)