I need to install iTunes for Mac OS Big Sur 11.3.1

Since Catalina, the functionality of iTunes has been subsumed by Music, TV, Podcasts and the Finder.

As dialabrain said, iTunes is not compatible, and it is not needed either.

If you have an iTunes music library, just open the Music application.

If you want to do something else, please elaborate.

iTunes is not compatible with Big Sur.

Hello,

@Luis, I have a similar need to have iTunes on Mac OS Big Sur 11.3.1.

I need to reset iPhone 6s. How can I do it without iTunes?

You can do this in Finder now

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Here’s the canonical support article for these macOS changes: What happened to iTunes? - Apple Support