How do I install iTunes on my Mac OS BiG Sur 11.5.2

iTunes was discontinued and replaced with other apps. It will not run on a Mac that is running Catalina or Big Sur. See: What happened to iTunes? - Apple Support

Since MacOs Catalina Itunes for movies have been moved to the Apple TV app, The music has been moved to the Music app, The podcasts moved to the podcast app, and the restore, update and other functions have been moved to the Finder. You can see it when you connected the device in the sidebar.

Apple Music is basically your new iTunes for the Mac.