The purpose of this study is to evaluate the safety, tolerability, and preliminary efficacy of MK-6837, administered as a monotherapy and in combination with pembrolizumab (MK-3475), in participants with histologically or cytologically confirmed advanced/metastatic solid tumors that have not responded to conventional therapy. There will not be any hypothesis testing in the study. As of Amendment 04 (effective date: 18-Dec-2025), there are no pharmacokinetic (PK) secondary outcome measures in this study.