iTunes library has disappeared since latest iMac update

Hi molly961,

welcome to the Apple (user-to-user) Community!

Re: "iTunes library has disappeared since latest iMac update"

Am no expert on iTunes or Apple Music, yet your questions certainly deserve some reply!

Seems iTunes is now part of the Apple Music app, and has been so for quite some time now.

(NB: The Apple Music app can be used with or without a subscription to Apple Music.)

As an intro to Apple Music: See: Add music to build your library in Music on Mac - Apple Support

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Re: "Since the updates to the iMac 2/3 of the music in my library has disappeared

... how do I retrieve the music I've been collecting for decades?"

If your Music was from your own CD's and etc... the folder of files may be still on your Mac,

If you wish, you can: Import songs from CDs into Music on Mac - Apple Support

or

You may be able to just open and play music files already on your Mac in the "QuickTime" app.

Else:

Wondering if you have a back-up of your music library, on your Mac, or on an external drive, (or perhaps via Time Machine to an external drive) etc. for safe-keeping.

If your Music was all from iTunes:

you may find it, (or be able to re-download it) in the Apple Music Library ?

Eg: Learn how to find and download music that you purchased from the iTunes Store

or

What to do: If there's an issue when you redownload apps, movies, or other content from Apple - Apple Support

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Resource:

Apple Music User Guide for Mac - Apple Support

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More help if needed: Music Support website: (info. / support / contact options etc.)

There is a "Get Support - start now" link at the bottom of their website.

Music - Official Apple Support

All the best :-)