Bring 5 cups water to a boil in a medium pot, season with salt, and add sorghum. Cover and cook until tender, about 1 hour. Drain well. Place racks in upper and lower thirds of oven and set a rimmed baking sheet on lower rack; preheat oven to 400°F. Arrange squash on another rimmed baking sheet; season with salt and dot with 2 Tbsp. butter. Place on upper rack in oven. Roast, turning occasionally to recoat with butter, until tender, 4045 minutes. Meanwhile, rub chicken all over with oil; season with salt and pepper. Place skin side down on heated baking sheet on lower rack in oven. Roast until an instant-read thermometer inserted into the thickest part of thigh registers 165°F, 3035 minutes. Cook remaining 4 Tbsp. butter in a large skillet over medium heat until it foams, then browns (be careful not to let it burn), about 5 minutes. Reduce heat to medium-low; add sorghum, squash, broth, maple syrup, and vinegar to brown butter and toss to combine. Simmer until liquid is evaporated, about 4 minutes. Remove from heat and stir in lemon juice; season with salt, pepper, and more vinegar, if desired. Divide squash and sorghum among plates and top with chicken, parsley, and pomegranate seeds.