A Study of the Safety and Efficacy of Various Combinations of Avelumab as Therapy in Locally Advanced or Metastatic Urothelial Carcinoma (JAVELIN Bladder Medley)

- Participants with histologically confirmed, unresectable locally advanced or metastatic urothelial carcinoma. Both transitional cell and mixed transitional/non- transitional cell histologies are allowed, but transitional cell carcinoma must be the predominant histology

- Participants has documented Stage IIIA/IIIB with N1-N3, or Stage IV disease (per American Joint Committee on Cancer/International Union for Cancer Control Tumor Node Metastasis system, 8th edition) at the start of first line chemotherapy.

- The last dose of first line chemotherapy must have been received no less than 4 weeks, and no more than 10 weeks, prior to randomization in the present study

- Estimated life expectancy of at least 3 months

- Participants without progressive disease as per RECIST v1.1 guidelines following completion of 4 to 6 cycles of 1L chemotherapy. Eligibility based on this criterion will be determined by Investigator review of pre chemotherapy and post chemotherapy radiological assessments (CT/MRI scans).

- Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0 or 1

- Adequate hematological, hepatic, and renal function as defined in the protocol

- Other protocol defined inclusion criteria could apply

- Participants with prior immunotherapy with Interleukin-2 (IL-2), IL-15, interferon alfa (IFN-α), or an anti programmed death receptor-1 (PD-1), anti programmed death-ligand 1 (PD-L1), anti PD-L2, anti CD137, or cytotoxic T cell lymphocyte-4 (CTLA-4) antibody (including ipilimumab), anti TROP2, anti-T-cell-immuno-receptor with Ig and ITM domains (anti-TIGIT) any other antibody or drug specifically targeting T cell costimulation or immune checkpoint pathways, agents targeting Nectin-4, or any of the investigational drugs used in combination with avelumab.

- Participants with active infection 48 hours before randomization requiring systemic therapy

- Participants with known prior or suspected hypersensitivity to study drugs or any component in their formulations

- Participants with prior adjuvant or neoadjuvant systemic therapy within 12 months of randomization

- Participants with vaccination within 4 weeks of the first dose of study treatment and while on trial is prohibited except for administration of inactivated vaccines (for example, inactivated influenza vaccines) administered >= 2 weeks prior first dose of study treatment. All severe acute respiratory syndrome coronavirus (SARS-CoV-2) vaccines approved or authorized by local Health Authorities are allowed

- Other protocol defined exclusion criteria could apply