This is pretty much canonical. Gygax didn't lean into it as heavily as Arneson did, but Blackmoor was pretty explicitly a post-apocalyptic setting, with remnant

This is pretty much canonical. Gygax didn't lean into it as heavily as Arneson did, but Blackmoor was pretty explicitly a post-apocalyptic setting, with remnants of advanced or alien technology being ubiquitous. Flying cars, laser guns, androids...