Looks like a newborn umbilical cord binder. Supposedly protects the umbilical cord while healing. Not really necessary, in my opinion.

https://www.amazon.com/ToBeInStyle-Babies-Comfortable-Newborn-Umbilical/dp/B08X6L3X1L?th=1&psc=1

u/Emotional_Salt3788 solved it with the comment above. Link to the original post

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