They programmed NAS music functionality out of the new app.

I don’t think that’s correct, as I can see/play my local NAS library in the new Sonos App… an SMB v2 (or higher) indexed share is required, as publicised on the forum and elsewhere, prior to the update.

I have found that the new Android app sometimes needs to be force-quit and restarted in order to display the various non-streaming sources (Line-in, Library, TV) under “Your Sources”. Try that and see if it comes back. You may well find the web app has it displayed already, look at https://play.sonos.com/en-us/web-app

When you can access it you’ll find the navigation is degraded, there is no cover art, you can’t play individual tracks from albums and it’s all excluded from search. Fixing these things is not mentioned in any of the updates Sonos issues so I am very concerned they are silently discontinuing the feature but that’s speculation.

I’ e lost my music library and have no option to add it. 

Customer “Service” told me to upload my 64 GB of audio to the web and use a commercial “Music Service” to stream it!

I can see my music library on the desktop app. And can get tracks to play from there, ONLY.

It’s not present at all on the android app though!

Even though if I start a track with the desktop app, it shows as playing on the android app.

I just don’t understand what’s going on here.

Something easy to try: “sign in” on the Android app (if you’re not already). I’ve seen that help make my local library visible.

I now see it on the Android app without me really doing anything. I can’t search for music but I can navigate through folders and play tracks. It’s a little clunky and slow but much better than a few days ago