OK — Gerard Butler is Scottish in real life. However, the character he plays in Last Seen Alive, loving husband Will Spann, is supposed to be American (although technically they never verify that in-universe, if you want to get really nit-picky).
Every other character in Last Seen Alive has an American accent, so we’re assuming that’s where the story is set!
Source: https://www.distractify.com/p/gerard-butler-accent-in-last-seen-alive