One of the big questions that I'm dealing with is post-retirement issues after FIRE, because no one really has a proper grip on the early retirement beyond financial figures, as successfully completing the FIRE journey is quite rare, and if only a few MBTI archetypes complete it  ( INTJ, ENTJ, ISTJ) even getting advice from folks who completed the journey might not create a complete picture on how to retire early systemically.

I have always harboured doubts that the answer can be found in books on personal finance, and I think I might even be better off looking at religious or philosophical texts.

Problems with early retirement are existential issues - they need a deep level of philosophical understanding to decode them. FIRE can barely solve 60% of your issues, as it can probably give you a level of personal satisfaction. But the remaining 30% comes from living a meaningful existence that FIRE cannot bestow. The final 10% is even more elusive, as it relates to psychological richness.