Can someone turn to God after they die?

The historic majority Christian position, held across most traditions, is no—Hebrews states plainly that "it is appointed for people to die once—and after this, judgment," presenting death as the boundary after which the opportunity for response has closed, not an intermediate stage with continued decision-making.

A minority of contemporary theologians have proposed the possibility of some form of opportunity after death, sometimes appealing to a genuinely difficult, debated New Testament passage about Christ making "proclamation to the spirits in prison." Most scholars, including many sympathetic to taking that passage seriously, read it as describing something else entirely—Christ's proclamation of victory, or his Spirit working through Noah in the past—rather than establishing a general doctrine of postmortem opportunity.

This remains a minority proposal rather than a mainstream position, and it's worth being honest that most historic Christian teaching holds this life as the time in which this decision is made.