My icloud photos won't upload onto my new macbook air 2018
You can try this found here:


  If your Photos library won't open, or if Photos behaves unexpectedly,
  the Photos library repair tool might resolve the issues.
  
  Follow these steps to use the Photos library repair tool:
  
  Hold down the Option and Command keys while you open Photos on your
  Mac. In the dialog that appears, click Repair to start the repair
  process. You might be asked to type in your user account password to
  authorize the library repair.
  
  The repair tool analyzes the the library's database and repairs any
  inconsistencies it detects. Depending on the size of your library,
  this might take some time. When the process is completed, Photos opens
  the library.