Why does My iPhone 11 pro not sync with my MacBook Pro? How do I repair it?

Set up iCloud on all your devices

To set up iCloud on your devices, sign in to each of them with the same Apple ID and password. You can choose which apps store information in iCloud and which iCloud features you’re using separately on each device

Is this a New Issue ? If Yes, what exactly changed on this computer ?

Is this an Old Issue ? If Yes, what actions has the user taken to fix this issue ?

Reliable , accurate, details and context will really help to pinpoint a possible solution.

Sync your iPhone, iPad or iPod using your computer – Apple Support (AU)