I installed this mod on my fabric server along with bfapi, and the config didn't generate. That was strange but I just created a file called lifesteal.json, pasted in the default settings and then changed them. Later I noticed that even thought I changed "looseHealthOnlyOnPlayerRelatedDeath" to true, whenever I died I still lost a heart.

Great mod though, thanks for making it :D

The config can be located with the general path mainDirectory/config/bfapi/*.json, for example lifesteals is mainDirectory/config/bfapi/lifesteal.json. I ask that you check there just encase as some people don't realise its in a sub folder of bfapi (I do this to stop conflicts with other mods with the same name).
If you still can't find the generated config can you send me your version details and a start log so I can look into this issue?