According to the instructions for surgical masks that meet Part 84 approval requirements, the masks are suppose to be kept out of direct sunlight until use..
Yes. They also are not supposed to be reused. Sunlight will degrade the elastic. I don’t care. Sunlight kills viruses, and I like that. I’m not a surgeon or even working with infected people, just a humble retired statistician. I’ll keep putting them in sunlight before reuse.