Is it true what is said that the fetus, while asleep in its mother's womb, sees its life cycle from birth until its death, and that a person's encountering situations they think they have seen before is due to that?

This statement has no proof from the Qur'an or Sunnah (definition), nor was it uttered by any trustworthy scholars. Matters of the unseen cannot be asserted with certainty except with conclusive proof. To claim them based merely on conjecture and speculation is invalid, as Allah says: "Say, 'Produce your proof.'" (Al-Anbiya: 24). The phenomenon of "seen before" was previously discussed in Fatwa (definition) no. 103863.