Can't access my music on iMac with Monterrey 12.7.6

It is in the account menu. See Authorize or deauthorize your computer for Apple Account purchases - Apple Support. That said if you still see such a message after authorizing the computer then it is usually a case of bad downloads.

I'm not clear if you already have either of the iTunes Match or Apple Music services, Apple's iCloud Drive service isn't really geared up to copy your library from one computer to another. If needs be see Recover your iTunes library from your iPod or iOS device - Apple Community in case you need to pull working copies of these tracks from your iPhone or iPad. The easiest method may be a temporary subscription to the Apple Music service, merging the music on your devices into an iCloud Music Library which you then download to your computer and backup for security.

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Repeated requests to authorize an already authorized computer for recent store downloads typically indicates you have corrupt or incomplete copies. Delete the tracks that won't play from your library without hiding from your purchase history. Redownload using the cloud links that should remain, or close Music and reopen if they don't show up straight away. While downloading click the activity widget and turn off the option that allows for simultaneous downloads.

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