There are such bags. They are called changing bags. Still, any windowless room (a pantry, a storage room, most bathrooms) will do the job with higher convenience.
If you do get a changing bag for this purpose, get the largest you can find. There are even changing tents that are much larger. They are designed for large-format photographers to load their film holders while traveling, but they are also useful for this purpose. Unfortunately the price is fairly significant.
Welcome. I think you'll find yourself to feel right at home here.