"While downloads will no longer be supported, you can continue to watch TV shows and movies offline on a supported mobile device," the Netflix document says
So essentially Windows devices are no longer "supported" wrt this particular feature.
It essentially means the Windows app will be little more than a wrapper for the Netflix website.
It's possible that the move means Netflix can save some money on licensing, which may cost extra if downloads are included – enabling users to take shows and movies around with them and watch them without an internet connection.
So once again everything devolves down to licensing - i.e. it sounds like they were pressured into this hard choice to leave those users in the cold, which they did. Probably bc the user base of Windows phones is so tiny? (Edit: bc they are discontinued, though more likely they meant the desktop - i.e. laptops - sorry if I caused any confusion).
Though that is one of the main advantages of Netflix these days, as opposed to e.g. piracy.
TLDR: Ultimately it is yet more enshittification, and while due to licensing rather than Netflix, still it is Netflix users (on Windows devices) who will bear the burden.
My advice would be to disable automatic updates and coast for a long while on the current app version, though that can be easier said than done due to multiple locations of automatic update settings. I have zero experience with Windows lately, but good luck if you want to try it!:-|