Trial Drug: Venetoclax

The purpose of this study is to assess the safety and tolerability and to confirm the dose of nemtabrutinib in combination with venetoclax in participants with R/R CLL/SLL. The primary study hypotheses are that the combination of nemtabrutinib plus venetoclax is superior to VR with respect to progression-free survival (PFS) per 2018 International Workshop on Chronic Lymphocytic Leukemia (iwCLL) criteria as assessed by blinded independent central review (BICR).