Hello, suzannefrommetairie.
Thank you for using Apple Support Communities.
From reading your post, it's understood your iPhone 11 Pro won't be recognized with iTunes on your Mac using OS X Yosemite. iOS 13 requires iTunes 12.8.2 or later which is supported on OS X El Capitan or later. You can check out this article to double check to see if you can update: How to upgrade to OS X El Capitan
If you can't update, OS X, you can look into using iCloud for backups as an alternative: How to back up your iPhone, iPad, and iPod touch
Let us know if you have any further questions.
Cheers!