Sin could usefully be defined as 'the condition of mortal life' - since that encompasses its two main aspects of wrong behaviour and death.
The Fall was therefore, primarily, moving into the condition of incarnated mortality - with its consequent inevitability of both death, and those behaviours that are a consequence of being imperfectly aligned with the divine will.
Reading the Fourth Gospel, we can see that the term 'sin' refers to a wider range of phenomena that more recent usage - in particular it is used sometimes to mean death; and by death is meant the ghostly, half-existence of demented souls that have been severed from their bodies, and wander 'witless' in the underworld that the ancients termed Sheol or Hades (later translated and reconceptualised as Hell).
The Fall refers to the choice and decision made by all of us mortal Men to leave the child-like, unfree, un-conscious Eden-paradise of our immortal pre-mortal spiritual life; where we were immersed-in God's will and lacking in personal agency - hence unable to act otherwise than in harmonious accordance with divine motivations.
When we became incarnated, we increased our free agency; but at the cost of becoming separated from God's will. Mortality (as a state) is characterised by change, corruption, disease and decay - as well as inevitable death.
Thus, no mortal Man (except for Jesus) has been fully aligned-with God's creation. We are all, therefore, 'sinners' in the dual sense of being not-fully-aligned with the divine will, and also destined to die.
However, The Fall is sometimes rightly described as a Felix Culpa - a blessed transgression; because it enables us to attain a higher level of divine nature.
Only after being separated from our previous state of unconscious immersion God's will; are we are (potentially) able to make the free choice of aligning ourselves eternally with God's will; and after mortal death, as resurrected eternal children of God, then actively-participating in God's work of ongoing creation - as ourselves gods.
(i.e. Small 'g' gods, working within God the creator's reality.),
(All this is made possible by our mortal incarnation, but we are free agents, so it is not guaranteed. Indeed, in the modern West, it looks like only a small minority are choosing to choose salvation and resurrection.)
At the same time, because we are not-fully-aligned with God's will in this mortal life, we will inevitably think, say and do many things that are opposed to God's will: that is, we will inevitably commit 'sins' in the more common usage of the word.
Those familiar lists of behavioural sins (e.g. the behaviours proscribed by the Ten Commandments, or the Seven Deadlys - or mortal and venial sins; or the Scriptural prohibitions from Paul's letters) can be understood as broad categories of behaviour that tend to be characteristic of those who are not-fully-aligned with God's will.
Behavioural sins (such as these lists) are therefore Not to be taken as 'sin-itself' - which is subjective; but observable 'signs' that are typically 'correlated-with' actual sin - sin itself being the mortal state of being unaligned with God's will.
The specific focus of these familiar 'behavioural correlates of sin' tends to be on those behaviours that are either especially tempting, or especially destructive of society in general or church order in particular. That is the reason why sexual correlates of sin are so prominent.
And this focus certainly seems to be necessary - in the sense that we can now observe the subversive effects of removing such restraints. The outcome has been moral inversion: i.e. the worst of all possible outcomes: the one most likely to lead to self-damnation.
However, on the flip side, there is a relative neglect and softness of attitudes to other types of more 'private' sin; such as envy, spite, cowardice, dishonesty and bearing false witness - which are in themselves probably more dangerous to the soul.
In sum; we are all Fallen in the sense that we will all die; and because our mortal lives are never fully-aligned-with God's creative motivations. And the inevitable difference between God's will and our own will leads to many thoughts, words and deeds ('sins') that are a consequence of this disharmony.
And the cure for sin - both mortality and behavioural disharmony - is on the other side of 'biological death'; when we may choose to be resurrected to Life Eternal in a condition of everlasting harmony with the divine work of loving-creation.