I was taught that prior to Christ’s dying and rising, people (in the Old Testament) could not enter heaven and see God. What about Abraham, Moses, Elijah, and the many holy women in the Old Testament?
You have identified a theological dilemma: how to speak about people who lived before Jesus as being saved without slighting the unique role of his passion, death, and resurrection. The concept of limbo was developed to cover this group of people, plus babies who die before Baptism—and ultimately good adults who were never baptized.
Limbo was never official Catholic doctrine, although some people have treated it as though it were. Jesus’ descent “into hell” (Apostles’ Creed) is really his going to the underworld to lead the souls of the people you referenced into heaven. The chora (“in the fields”) church in Istanbul, Turkey, has an impressive fresco (above) of that scene.