Can I download iTunes on 11.4 Big Sur?

With the macOS loaded, you already have the iTunes app loaded.

iTunes was broken into several apps a few generations of macOS ago.

Today those apps are called TV, Podcasts and Music.

You should be looking for the Music app.

EDIT - the fourth app split from iTunes is Books.

In Mojave and earlier it would be appropriate to use iTunes to sync your iPhone as per the link you posted.

In Catalina and Big Sur, the iPhone is now synced using the sidebar of a Finder window.

Here's a link to getting it done this way –

Use the Finder to sync your iPhone, iPad or iPod with your computer - Apple Support:

https://support.apple.com/en-us/HT210611

You're welcome. 🙂

The only comment is - it is not relevant. The supplied link refers to running Mojave ( Released September 2018 ) and below. According to your posting - the computer is running Big Sur. All that @ D.I. Johnson has outlined pertains to Catalina and Big Sur.