Their "copy something from precursor technology" world building point itself being a copy of precursor technology (Mass Effect in this case)? How meta! Maybe Emil Pagliarulo is a clever writer after all. /j

Testing the FTL drive fucked up Earth's magnetosphere and it's uninhabitable now

But space

In one of the last missions, you learn from audio logs at an abandoned NASA facility on earth that the guy who "created" the warp drive did so having learned how to from some magic precursor artifact. Due to the artifact, he also knew that using it would destroy the magnetosphere of the planets it was used around over time. He also knew that doing so would result in only a few million people being able to evacuate earth before it became uninhabitable and therefore he was sentencing 99+% of humanity to death. He did this anyway because "going to space is just so important". There is no actual reason ever given in game for why someone would actually want to go to space because frankly space in Starfield is boring as fuck.

To make things even worse, he also knew that this fundamental flaw in FTL tech would actually be solvable with a software patch but didn't deploy it because I guess he just wanted to be the worst genocidaire of all time.

To make things even more worse, IIRC THE GAME NEVER ACTUALLY ADDRESSES THAT HE DID THIS. You have to read between the lines that this random engineer is history's greatest monster.