Well, the new trend of 2020 is a "nap dress" and apparently it's VERY different from a nightgown.
According to Today:
There are certain qualities that define a nap dress. They're usually made of soft, breathable material and have an ethereal or special quality to them that makes them feel different than wearing an ordinary dress. While they're as comfortable as a nightgown, they also include extra touches, such as lace and smocking that make them look stylish enough to wear from bed to brunch.
Arguments are being made that Taylor Swift even rocked a "nap dress" for pictures of her new album, Folklore.