A Study to Evaluate CRB-701 Compared to Investigator's Choice Therapy in Previously Treated Oropharyngeal Squamous Cell Carcinoma

The goal of this study is to understand whether CRB-701, a targeted form of chemotherapy called an anti-body drug conjugate, will work as a treatment for oropharyngeal (throat, tonsil) cancer. In patients who have already received platinum based chemotherapy or immunotherapy (using a check-point inhibitor) It will also learn about the safety of the drug and measure quality of life. The main questions it asks are: * What proportion of participants respond to CRB-701 measured using scans (CT or MRI) * What medical problems do participants experience when taking CRB-701. Researchers will compare CRB-701 with standard of care medicines (drugs that are normally used this disease). Participants will: * Attend clinic every three weeks to receive infusions of CRB-701 or standard of care medicines until the cancer cannot be measured or is not controlled by the treatment they are receiving. * Have a CT or MRI every 6 weeks to measure the effect on their cancer * Complete questionnaires to assess their health status.