No decision was made to “remove library support”.  So you are starting from a false premise.  Instead, they removed support for two share protocols due to security risks (not to mention a 200 page thread of chicken little posts complaining about those security risks).  Any issues with the new sharing methods were solved months ago, and the instructions on how to use the SMB v2/v3 protocols are right here:

https://support.sonos.com/en-us/article/add-your-music-library-to-sonos

Hi I use the local library quite a bit, I am running it on a Synology NAS. I think it is a great feature but needs some development to make it really useful. Firstly support for Atmos streaming, I have proved it works in DD+  JOC  in an mp4 container but I am told it's not officially supported. Secondly support for TrueHD plus Atmos in either an mkv of mp4 container.

Roger

The setting for sharing music files from my phone doesn't work in the sonos app. It's asking for the path to my sd card using the format //computer name/shared path but whatever I input, it will just tell me the path is unavailable or powered off. I'm assuming it's something like //storage/music. 

As has been explained in many threads and posts, Sonos no longer has direct access to music stored on iOS and Android devices, due to restrictions made by the creators of the respective OS. In order to ‘play’ directly from a phone, you’ll need a Sonos device that supports either AirPlay 2 or Bluetooth, and a player on the phone. You’d then set the output of the player on the phone to use the connection to the Sonos, via AirPlay 2 or Bluetooth, which then is sent to the Sonos, skipping the Sonos controller.