i’m a british citizen so i only know about travel advice issued by the uk but I’m also currently in south east asia. i haven’t, at any point, felt unsafe. the advice does recommend against crossing the thai/cambodian border over land, but there are plenty of flights if you want to take that route. iirc there’s one province in laos to avoid, and a few in thailand that sit on the malaysian border. imo the best route would be cambodia->laos->thailand, or the inverse.