At this point your logic board likely has a problem within the power logic.
A common issue I encounter is damage caused by a fake charger. Different MacBook series encounter different areas damaged as Apple has improved some areas over the years which then pushes the weak point to a different area in the logic.
Are you able to dig into the schematics and have the needed tools and part to fix the logic board or is replacing it the easier solution? [guide|38529] I would recommend following [https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w|Louis Rossmann’s YouTube channel] as he has some great vids that get into the process he goes through to diagnose and repair logic boards.