Evaluation of Co-formulated Pembrolizumab/Quavonlimab (MK-1308A) Versus Other Treatments in Participants With Microsatellite Instability-High (MSI-H) or Mismatch Repair Deficient (dMMR) Stage IV Colorectal Cancer (CRC) (MK-1308A-008/KEYSTEP-008)

Inclusion Criteria: * Has a histologically confirmed diagnosis of Stage IV CRC adenocarcinoma (as defined by American Joint Committee on Cancer \[AJCC\] version 8) * Has locally confirmed dMMR/MSI-H * Has a life expectancy of at least 3 months * Female participants are eligible to participate if not pregnant or breastfeeding, and not a woman of childbearing potential (WOCBP), or if a WOCBP then uses a contraceptive method that is highly effective or is abstinent on a long-term and persistent basis, during the intervention period and for at least 120 days after the last dose of study intervention * Has measurable disease per RECIST 1.1 as assessed by the site and verified by BICR * Submit an archival (within 5 years of Screening) or newly obtained tumor tissue sample that has not been previously irradiated; formalin-fixed, paraffin embedded (FFPE) blocks are preferred to slides. * Has adequate organ function Cohort A: \- Has been previously treated for their Stage IV dMMR/MSI-H CRC and radiographically progressed on or after or could not tolerate standard treatment, which must include all of the following agents if approved and locally available in the country where the participant is randomized: * Fluoropyrimidine, irinotecan and oxaliplatin (capecitabine is acceptable as equivalent to fluorouracil in prior therapy) * With or without an anti-vascular endothelial growth factor (VEGF) monoclonal antibody (e.g., bevacizumab) * At least one of the anti-epidermal growth factor…