A Study to Investigate Safety and Effectiveness of BGB-16673 in Combination With Other Agents in Participants With Relapsed or Refractory B-Cell Malignancies

Key Inclusion Criteria: * Must sign the informed consent form (ICF) and be capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the ICF * Confirmed diagnosis of a R/R B-cell malignancy * Protocol-defined measurable disease * Stable Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 2 * Adequate organ function * Female participants of childbearing potential must be willing to use a highly effective method of birth control and refrain from egg donation for the duration of the study and for ≥ 7 days after the last dose of sonrotoclax, 30 days after the last dose of BGB-16673 or zanubrutinib, 60 days after the last dose of glofitamab, or 90 days after the last dose of mosunetuzumab. A negative urine or serum pregnancy test result must be provided 10-14 days before the first dose of study treatment * Nonsterile male participants must be willing to use a highly effective method of birth control and refrain from sperm donation for the duration of the study and for ≥ 7 days after the last dose of sonrotoclax, 30 days after the last dose of BGB-16673 or zanubrutinib, 60 days after the last dose of glofitamab, or 90 days after the last dose of mosunetuzumab * Substudies 1, 3, and 4 Inclusion Criterion: * Adequate renal function as indicated by estimated glomerular filtration rate (eGFR) of ≥ 50 mL/min * Substudy 2 Inclusion Criteria: * Bruton tyrosine kinase (BTK) inhibitor-naive, or previously received treatment with a covalent BTK inhibitor and discontinued for reasons other than clinical progression * Adequate renal function as indicated by eGFR of ≥ 30 mL/min Key Exclusion Criteria: * Treatment-naive B-cell malignancies * Unable to comply with the requirements of the protocol * Active leptomeningeal disease or uncontrolled, untreated brain metastasis * Any malignancy ≤ 2 years before first dose of study treatment except for the specific cancer under investigation in this study or any locally recurring cancer that has been treated curatively * Autologous stem cell transplant ≤ 3 months prior to screening or chimeric antigen T-cell therapy ≤ 3 months prior to screening * Prior invasive fungal infection, except if participant agrees to receive secondary antifungal prophylaxis during the entire treatment period * Substudies 1 and 2: Prior allogeneic stem cell transplant with active graft-versus-host disease (GVHD), or requiring immunosuppressive drugs for treatment of GVHD, or who have taken calcineurin inhibitors within 4 weeks prior to consent * Participants who have a history of severe allergic reactions or hypersensitivity to the active ingredient and excipients of BGB-16673, sonrotoclax, zanubrutinib, mosunetuzumab, or glofitamab * Substudy 1 Exclusion Criterion: * Prior treatment with a B-cell lymphoma-2 (Bcl-2) inhibitor (with exception for participants who relapsed ≥ 24 months after completion of a full course of a prior Bcl-2 inhibitor containing regimen) * Substudy 2 Exclusion Criterion: * Participants who discontinued prior zanubrutinib treatment due to intolerance * Substudies 3 and 4 Exclusion Criteria: * Prior exposure to a CD20 x CD3 T-cell engager antibody treatment * All participants with a prior allogeneic stem cell transplant * Participants with known contraindications to azole antifungal agents, including hypersensitivity reactions Note: Other protocol defined Inclusion/Exclusion criteria may apply.