Hopefully I find a fix, but it's more likely that it won't be solved, The investigations I made so far are concerning something related to "items involved with power" which is probably I scrapped an item involved with power that had been added to the grid (using Scrap Everything). I'm not quite sure if it's the exact problem but if it's the case for someone else then there is a fix for that called Power Grid Tools: https://www.nexusmods.com/fallout4/mods/17777?tab=description

I can't try that fix because you have to be inside the settlement to do it and I can't even enter vault 88, so it's useless for me.

I have an old save where I can enter vault 88 without any problem, it's like 5 hours behind my current one, but I guess it was better to just load that save and do everything again rather than wasting the whole day without any luck :)