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?

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.

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.

Typically roommates have their own rooms. Sometimes that's not the case.

Neither one. It could be a separate room with a shared kitchen.