As a member of an admissions committee, I can tell you this is generally false. The school you attend is factored in in my STEM field… to a point. If everything else on your application is stellar, then it doesn’t matter where you got your BS; you will still get into many graduate schools. If you are a borderline candidate, then the school you attend can matter since faculty on the admissions committee are more likely to give you the benefit of the doubt if you came from a program they know and respect.