The goal of this clinical trial is to understand if a new drug called LNS8801 can safely treat patients with melanoma. The primary question to be answered is what is the average length of time during which melanoma does not grow or spread after starting treatment with LNS8801? Researchers will compare LNS8801 taken alone or LNS8801 taken together with another drug called pembrolizumab to other therapies as decided by the treating doctor. 135 patients will be randomly (like flipping a coin) placed in 3 treatment groups. In the first group (LNS8801 only) - Patients will take 125mg tablet of LNS8801 by mouth once per day every day for up to 2 years. In the second group (LNS8801 + pembrolizumab) - Patients will take 125mg tablet of LNS8801 by mouth once per day plus 200 mg of pembrolizumab by IV infusion once every 3 weeks for up to 2 years. In the third group, called Physician's Choice (PC), patients will receive chemotherapy (dacarbazine or temozolomide) or immunotherapy (pembrolizumab, nivolumab/relatlimab or nivolumab/ipilimumab) as determined by their treating physician. How often the patient visits the clinic visits will depend on the treatment group. Besides returning to the clinic for treatment, the patient will undergo periodic safety assessments and other required study procedures such as imaging assessments.