How do I make the user's 'library' folder within a Time Machine backup available to 3rd party apps? As many users know, the Library folder located within a User's Home directory is hidden in recent versions of macOS. And, to make this visible, the user can hold down the Option key while accessing the Go menu from within the Finder.

In terms of Time Machine backups, the same Library folder is also hidden from view. Users can make these visible within the Finder by making 'hidden' files visible and navigating around their Time Machine backups.

However, what I am looking for is a way to make this same folder (i.e. the user's home 'library') on Time Machine backups visible to 3rd party applications. 

By way of example, let's say I wanted to use data recovery software to import an old iOS iTunes backup located within a Time Machine backup, how would I do this? 

Making the folder visible within the Finder does not help, although I could then manually copy it from the TM backup drive onto another disk and import it from there, but I'm looking for a more convenient/elegant solution if one exists?
As the latest backup is always going to be in the same place, then it's going to be the same path as ~/Library, plus the TM path.

Regular path is ~/Library/Application Support/MobileSync
or longhand Volumes/[boot drive]/Users/[user name]/Library/Application Support/MobileSync
so in Time Machine it will be
Volumes/[TM drive]/Backups.backupdb/[mac name]/Latest/[boot drive]/Users/[user name]/Library/Application Support/MobileSync

Your larger problem may be that the folders in there have special permissions rwx------ &amp; you cannot get any further than Library using Go to Folder... from the Go menu.