Dear Ps, I certainly understand your point about the difficulty of the problem of evil and the impact that has on belief. There are very rational attempts at responding to this question, if interested, Alvin Plantinga is the probably the best among contemporary philosophers. However, the statement that Christianity is in retreat isn't quite accurate. Certainly we are seeing a major change and even a retreat of some kind in the US, but here is what AI says about the growth of Christianity today:

The number of Christians is expected to grow from 2.52 billion in 2024 to 2.63 billion, and then to over 3 billion by 2050. This is a 1.08% growth from 2024 to 2025.