Windex is crap, I do not have very good luck with it removing the thin film layer on the inside of windows ChrisFix, a pretty good YouTuber, has a video on how to “Super Clean” the inside of your windshield:
It’s a 7 minute video, but the TLDR is: Use a dry microfiber towel, then clean with either rubbing alcohol or a magic eraser, then follow up with a good glass cleaner like Invisible Glass. He also explains where the film comes from and why you need to repeat this process every so often.
Also, I would recommend putting some towels on the dash itself before starting, that will prevent any drips from staining the dashboard, especially if you’re using rubbing alcohol, which can discolor plastics, vinyls, and leathers on most dashboards.