Coincidentally, I experienced a posterior vitreous detachment in 2020, a year after this thread began. I noticed the symptoms during a nighttime bike ride, when there were distant thunderstorms, far enough away to be barely visible in the far western sky. But on my return trip home I continued to notice what appeared to be lightning flashes from the outer corner of my left eye, which at this time was facing east, away from the thunderstorms.
By the time I got home I realized it was my left eye. A few hours later the vision was cloudy and grainy in the left eye. The next morning I phoned for an ophthalmology appointment and was fortunate to get in a day later. This was early in the pandemic, before in-person non-emergency medical appointments were very difficult to get.
The ophthalmologist (dressed head to toe in hazmat-quality PPE, including a surgical mask over an N95-type mask with an exhalation vent, which was all they had available) said it was probably just age-related (I was 62 or 63 at the time) and did not appear to be related to my bicycling or exercise routines. Unfortunately, he said it will probably be a recurring problem and there isn't much they can do to prevent or treat it, but it shouldn't need medical intervention.
That particular bout with PVD cleared up within a couple of weeks. It recurred occasionally to a much lesser extent for the next year. No problems in several months.