Unsyncing iOS from Desktop

ALittleNutty wrote:

My iOS device is an iPhone XR and was synced to my old MacMini, but now I want to unsync them.

Please use the same process to Sync with your new PC/Mac. See how to --> Sync your iPhone, iPad, or iPod using iTunes on your computer ...

You will get an alert that you already have another Mac/PC synced to this device (iPhone).

You will get an option to continue with this PC/Mac.

You will again be prompted that all Photos and Videos synced from your Old PC/Mac will get deleted from the iPhone.

If that is what you want! Choose OK.

Though I am not vrey clear in interpreting your need however, ...

Have synced few Photos from your Mac/PC through iTunes. UN-sync then they would be gone from iPhone.

UN-Sync photos to your device

1. Connect your device to your Mac.
2. You can connect your device using a USB or USB-C cable or using a Wi-Fi connection. To turn on Wi-Fi syncing, see Sync content between your Mac and iPhone or iPad over Wi-Fi.
3. In the Finder  on your Mac, select the device in the Finder sidebar.
4. 
5. Select Photos in the button bar.
6. 
7. Note: When iCloud Photos is turned on, no photo syncing options appear when you select Photos in the button bar.
8. Select “Sync Photos to your device from” tickbox, then choose Photos, Pictures or a folder from the pop-up menu.
9. 
10. Uncheck Sync photos
11. Click on Apply / Sync