Foggy vinyl windows may be caused from UV as well as mold and algae growth (white powder look).
Cleaning with acid may solve problem but practice is intrusive because it removes oil in panel (vinyl or polycarbonate) which may exacerbate problem.
If mold, clean with mild solution of bleach, and then replenish the oil in panel.
For example, some drivers use olive oil to polish the lens in instrument panels.
I use Lemon Pledge (yellow aerosol can) to clean, replenish and protect the windshield on my motorcycle.
When I was a detailer, I used Pledge to de-fog the vinyl windows on convertible tops and Jeeps.