How to load a massive amount of data into Photos on a Mac set to Optimize Mac Storage

Your Mac has 128GB of storage and you have 600GB of photos. What to do?
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Apple
    Related:
  • Photography
  • Productivity Software
  • iCloud
  • Mac
  • iCloud Photo Library
Glenn Fleishman’s most recent books include Take Control of iOS & iPadOS Privacy and Security, Second Edition (covering iOS 15/iPadOS 15), Take Control of Your M-Series Mac, and Take Control of Securing Your Mac. In his spare time, he makes Tiny Type Museums. He’s a senior contributor to Macworld, where he writes Mac 911.