Does anyone know what this is? Just started growing on my 6 mo. Boxer female doesn’t seem to bother her as of yet

Growths could be caused by any number of things, some benign and some dangerous to your dog's health. It's impossible to tell what's going on with your pup, specifically, without proper medical diagnostics, so you definitely need to have your vet look at it and help you decide what your next step should be.