value of a post baccalaureate certificate for phd admissions?

so essentially, if i do not get into any of my top choices, i am thinking of doing an engineering focused post bacc and then applying to a mix of applied math and engineering phds. will this give me any upside or would it be a waste of time/money?

for context, my undergraduate degree is in pure math with a lot of numerical math electives. i realized i preferred the applied route a little too late to pivot completely.