This study is being done to answer the following question: Will erdafitinib treatment be able to shrink or slow the growth of brain cancer that has returned or gotten worse after treatment? This study is being done to find out if treatment with erdafitinib is better or worse than the usual approach for your brain cancer. The usual approach is defined as care most people get for brain cancer: treatment with surgery, radiation, or FDA-approved drugs such as lomustine or bevacizumab. Sometimes, combinations of these treatments are used. Are you Eligible? (Inclusion Criteria) Are you 18 years of...