The initial release of Photo Mechanic 6 did not include the "Search my Mac" feature from previous versions of Photo Mechanic. "Search my Mac" returned with Photo Mechanic 6 build 4484, released in April 2020 and is available in all subsequent builds of Photo Mechanic 6 and Photo Mechanic Plus.
"Search my Mac" utilizes Spotlight to find images on your computer and connected drives to and display them on a Contact Sheet.
You can now find Spotlight search above the Navigator/Favorites Panel on the left side of the Photo Mechanic Contact Sheet window on the MacOS version of Photo Mechanic 6 and Photo Mechanic Plus: