OK I have a couple of windows like this, Basically the insulation bit of the gas in the window has failed, and you get “stuff” inside it. Like the author, the windows themselves are OK, and are a custom “large” ones that will be very expensive to fix. This could be a good alternative to clean them up.
https://www.instructables.com/Cleaning-a-FoggyHazy-Window-Insulated-Glass-Unit-I/