This clinical trial is for adults who have been diagnosed with one of the following relapsed or refractory (R/R) B-cell malignancies: non-germinal center B-cell diffuse large B-cell lymphoma (non-GCB DLBCL), follicular lymphoma (FL), Richter’s Transformation (RT), Waldenstrom macroglobulinemia (WM), marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), or chronic lymphocytic leukemia / small lymphocytic lymphoma (CLL/SLL).
   
The purpose of this study is to test if the drug BGB-16673 is safe and if it works in participants with relapsed or refractory (R/R) B-cell malignancies when it is given in combination with other study drugs across four separate substudies. The study doctor will discuss with participants which substudy they will participate in based on their disease histology and prior treatment history.
   
The theory behind this clinical study is that BGB-16673 used in combination with other drugs may work better when given together to increase the number of participants who respond well. The study drug combinations participants will receive in this study have not been approved by the United States Food and Drug Administration (FDA) for the treatment of their disease.
   
In SUBSTUDY 1, participants will receive BGB-16673 combined with sonrotoclax. BGB-16673 will be taken orally once daily starting from Week 1 Day 1. Sonrotoclax will be taken orally once daily starting from Week 5 Day 1.
   
In SUBSTUDY 2, participants will receive BGB-16673 combined with zanubrutinib. BGB-16673 will be taken orally once daily starting from Cycle 1 Day 1. Zanubrutinib will be taken orally once or twice daily as instructed by the study doctor, starting from Cycle 1 Day 1.
   
In SUBSTUDY 3, participants will receive BGB-16673 combined with mosunetuzumab in repeats of 21-day study treatment cycles. BGB-16673 will be taken orally once daily starting from Cycle 1 Day 1. Mosunetuzumab will be administered as an injection under the skin at the clinic by qualified staff 3 times during Cycle 1 and then once per cycle for subsequent cycles.

In SUBSTUDY 4, participants will receive BGB-16673 combined with glofitamab in repeats of 21-day study treatment cycles. BGB-16673 will be taken orally once daily starting from Cycle 1 Day 1. Glofitamab will be administered as an intravenous (in the vein) infusion at the clinic by qualified staff 2 times during Cycle 1 and then once per cycle for subsequent cycles. Participants will also receive a pretreatment of obinutuzumab intravenously once on Cycle 1 Day 1.

Participants can continue to take the study drug treatment until their disease worsens, they experience unacceptable side effects, they or their study doctor decide they should stop, they meet other study discontinuation criteria, or cancellation of the study. After participants have permanently stopped study drug treatment, they will enter the follow-up phase of the study for as long as the study is ongoing (unless they decide to withdraw consent). Overall, participation in the study is likely to last about 3 years and approximately 29 visits.