When an American says they have roommates, do they literally mean they share a bedroom with another adult they're not romantically involved with? Or does 'room' mean the whole apartment?
Neither one. It could be a separate room with a shared kitchen.
Shared kitchen and bathroom. It's not ideal, but it's also not worth paying twice as much in rent for exclusive use of those two rooms that I only need for an hour a day or less.
Typically roommates have their own rooms. Sometimes that's not the case.
In college, everyone used roommate for someone in the same bedroom and apartment-mate or suite-mate for someone in the same unit. For us, a suite lacked a kitchen and living room, but did share a bathroom.
As others have said, roommate generally just means living in the same apartment. It's a weird term though, in that I wouldn't use "room" to refer to an entire apartment.