Chemotherapy for lymphoma can cause side effects, especially in people age 65 and older and those with other health problems. Researchers want to see if adding the immunotherapy drugs glofitamab, polatuzumab, and obinutuzumab to treatment can reduce the amount of chemotherapy needed. The people in this study have diffuse large B-cell lymphoma (DLBCL), high-grade B-cell lymphoma (HGBCL), or transformed lymphoma. Their cancer has not yet been treated.