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.
