Glad to see you on here again. Your honest struggles are always welcome on the Forum.
All science can talk about is scientifically detectable purposes. This is the realm of so-called methodological naturalism. It cannot talk about or rule on purposes that lie outside the detection of the scientific method.
Your description of evolution crosses the line into metaphysical or ontological naturalism, i.e., saying that there is no purpose, not merely that it’s not scientifically detectable. Science does not and cannot affirm ontological naturalism.
Not sure if this will be helpful, but one thought experiment I like to give of this sort of undetectable purpose, a sort of natural miracle, is the pastor who has a particular financial need, and he prays about it, and the next day he finds an envelope under his door mat with exactly that much money in it. Now, clearly, a parishioner felt prompted to give this; God didn’t miraculously create authentic American dollars with E Pluribus Unum and all ex nihilo.
No scientist would ever be able to determine that this gift was an act of God. As far as she is concerned, it is a coincidence, or at least ascientific. But can we believe that God, through means that we don’t fully understand, gave inner promptings to the generous parishioner to give of his resources to the pastor? Absolutely. This is a purpose that we cannot detect scientifically; it is personal in nature and very real.
In sum, there are many different kinds of purposes: some detectable scientifically, some not. Does that help?