Good morning! Just wanted to let you know that the issue seems to be resolved for me. I had /e/ OS on my FP 4 and finally decided to reinstall Fairphone OS with Android 13. Here are the instructions I followed: flashing with fastboot. I did this yesterday evening and the FP 4 only lost 4% of battery overnight with everything turned on (only do not disturb activated).
I am no expert, but this may actually be more than just a factory reset. Also, note that I encountered the issue while using /e/ OS, so this may not relate to the issues you observe.