It seems clear that Catholic Church debunked Origens claim that souls were created and existed before conception and birth.
That is not as clear as you suggest, and certainly the soul is there before birth according to current teaching of the RCC. Current teaching looks like "at the time of conception" per the following:
The Catechism of the Catholic Church (Article 2270, in English):
2270 Human life must be respected and protected absolutely from the moment of conception.
From the first moment of his existence, a human being must be recognized as having the rights of a person - among which is the inviolable right of every innocent being to life.
Before I formed you in the womb I knew you, and before you were born I consecrated you.
The Italicized portion comes from Jeremiah 1:5.
The above extract is a subset of a longer discourse beginning in article 2258 about life and not taking innocent life, per the Fifth commandment, which then goes to abortion and euthanasia and suicide and more. The "before I formed you in the womb" stands out, when combined with earlier articles in the Catechism that presents the soul:
365 The unity of soul and body is so profound that one has to consider the soul to be the "form" of the body i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man, are not two natures united, but rather their union forms a single nature.
366 The Church teaches that every spiritual soul is created immediately by God - it is not "produced" by the parents - and also that it is immortal: it does not perish when it separates from the body at death, and it will be reunited with the body at the final Resurrection.
From that combination, the meaning comes across as either that
the soul was known to God before conception, or
that the soul and physical being/body are joined at the time of
If I had to choose one of the two, go with the latter as the articles feel more explicit in terms of the official teaching. The passage in Jeremiah could be taken as "formed in the womb" being the entire process of gestation before birth ... if that's the meaning intended, it would marry up with the latter pretty well.
Final Answer: based on the Catechism, at time of conception.
A Difficulty / Postscript
When you get to ideas and doctrines like God being omnipresent and thus unbound by time, the whole idea of a "before" for God loses meaning. This could lead to God knowing you as being unbounded by time at all stretching into infinity/eternity in both directions and thus more or less "before conception." Interesting as a line of inquiry, but not helpful to answering your question. The Catechism tries to make things more understandable, not less so. (Though it success on that score varies).