Plenty of animals do - multiple reptiles fish, birds, mammals, insects, arachnids, other bugs

 

IMPORTANT DETAIL ABOUT THE ORIGINAL STUDY

The original study claiming platypuses are biofluorescent used dead platypuses (2020) - I couldn't find more recent research with live subjects

 

This can make a difference as various bacteria, fungi and other organisms are biofluorescent under UV, so a corpse could also be covered in those organisms. But again, some other mammals showcase Biofluorescence. Reasons are simply how the higher energy wavelengths of light is absorbed by the fur - it may not have an actual ''reason'' or ''use'' - it is probably just the way it is, but some experts suggest it might've been related to survival with a distant ancestor - it could've made predation from certain predators more difficult, a form of camouflage (but nothing really supports that theory)