where is the search button in itunes

In the Music app on a Mac? If so, it is at the top of the sidebar on the left. After clicking in the search box, select iTunes Store at the top right of the main window. See the screenshot below from Buy music from the iTunes Store - Apple Support

In iTunes at the top Right corner:

In the Music App at the top left corner:

In Music a more useful search tool for your library crops up if you use View > Show Filter Field.

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