That’s an interesting paper! Although it seems a bit confounded—“Because eyes of mice and of human volunteers were not covered, we cannot exclude the possibility that solar/UV radiation to the eye affected the observed sexual behavior.” Which would be interesting if true, suggesting that just being outside and getting UV light in the eyes would be the thing to do. I guess you note this at the end of your first comment.
What do you think about the potential skin aging effects of UV vs the potential health benefits?
https://www.sciencedirect.com/science/article/pii/S1015958423001392 suggests that bright light might be causing the effect, not UV.