Blight on winterberry leaves
While we cannot positively identify the ailment from the photo, there are a number of leaf-spotting diseases common to foliage this late in the season that are not impactful on overall plant health. Symptoms from environmental stresses can also mimic disease and be challenging to differentiate. Infections that took place earlier in the season (usually in wetter and/or cooler weather) can be asymptomatic until late-season cumulative stress causes leaf damage. As the leaves will be shedding soon, nothing needs to be done except to keep the plant in overall general good health. For winterberry, this means simply not letting them experience prolonged drought without supplemental watering, as they thrive in evenly-moist soil. Since we have experienced autumn droughts before (just last year, actually), this means monitoring for soil moisture should continue up until the surface of the soil starts to freeze, or until all leaves are lost and frosty evenings are common.