I have a iPhone 8 and my Mac Desktop. iTunes does not recognize my iPhone when I connect it.

Yours is the oldest version of OS X and iTunes that might recognize this iPhone.

If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support

“iTunes”? That means you have an old operating system, as iTunes hasn’t been on Macs for a while.

Tell us:

• Your iOS version number
• Your OS X name and version number
• Your iTunes version number
• The model and year of your Mac