This substudy is part of an umbrella platform study which is designed to evaluate investigational agents with or without pembrolizumab in participants with urothelial carcinoma who are in need of new treatment options. Substudy 04A will enroll participants with locally advanced or mUC whose disease is resistant to treatment with programmed cell death-1/ligand 1 (PD-1/L1) inhibitors. The protocol infrastructure will enable the rolling assignment of investigational treatments.