A Study to Evaluate Safety and Clinical Activity of GSK5926371 in Adult Participants With Relapsed or Refractory B-NHL

Inclusion Criteria: * Has histologically confirmed Relapsed/Refractory (R/R) B-NHL, for which systemic treatment is indicated, 1. Has measurable disease, 2. Has received at least 2 prior lines of systemic anti-neoplastic therapy, including an anti-CD20-containing combination appropriate for the indication; 3. Has documented disease relapse, progression or disease refractory to the most recent line of therapy, per Lugano criteria.: * Willing to use adequate contraception (Participant of childbearing potential \[POCBP\] only). * Is capable of giving signed informed consent * Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. * Has adequate organ function. Exclusion Criteria: * Has a malignancy (except disease under study) that has progressed or required active treatment within the past 24 months except for basal cell or squamous cell carcinomas of the skin or in-situ carcinomas (e.g., breast, cervix, bladder) that have been resected with no evidence of metastatic disease. * Has had any major surgery within 4 weeks prior to the first dose of GSK5926371 or has not recovered from prior surgeries or complications. * Has a history of Progressive multifocal leukoencephalopathy (PML), current central nervous system (CNS) involvement by lymphoma, or a history of significant CNS disease such as uncontrolled seizures, stroke, epilepsy, CNS vasculitis, and neurodegenerative conditions. * Has an active uncontrolled infection. * Has received a prior Allogeneic stem cell transplant (allo-SCT) within 12 months prior to the first dose of GSK5926371 or has active graft-versus-host disease requiring systemic immunosuppressive therapy. * Has received a prior autologous stem cell transplant within 100 days prior to the first dose of GSK5926371. * Has received prior treatment with Chimeric antigen receptor T-cell (CAR-T) therapy within 12 weeks of first GSK5926371 administration. * Has received prior treatment with CD19- or CD20-targeting Bispecific antibody (BsAbs) within 8 weeks of the first dose of study intervention. * Has QT interval corrected (QTc) \>450 milliseconds (msec) or QTc \>480 msec for participants with bundle branch block. * Has significant cardiovascular disease such as uncontrolled arrhythmias, Class 3 or 4 congestive heart failure as defined by the New York Heart Association Functional Classification, ejection fraction \<=45% by any methods in the 12 months of enrollment, unstable angina or acute coronary syndrome including myocardial infarction within 6 months of enrollment.