Chosen Solution

Already tried hard reset, different charger and battery replacement, still nthing has changed. Any idea what to do? I have some experience with microsoldering.

I usually don’t say this but go to apple. AFAIK apple has a replacement program for iPhone 8 that randomly shuts down. And maybe if it has been exposed to helium (like if you’ve just been from a hospital) then wait a week for it to turn back on.