my brother swears by just using a damp [water only], used soft T-shirt to "clean", then dry with another used, soft T-shirt.
his windows are always clear. i don't know how he came up with this method. he doesn't smoke, so that helps a bunch.
i have, over the years, found that the plastic in vehicles [going back mucho years] "outgasses". this causes glass to fog, smear, or cause something of a cloudy appearance, requiring frequent cleaning. newest vehicles seem to be worse than older ones, and some do this process [outgassing] more than others. as it will never [seem to] quit, it will slow down [some or a lot] as the plastics age.
i learned about that in a class taught at work, where we were having a problem viewing through a glass lens at internal components made of plastic.