Putting this here in case I forget it later and Google it again.
In my case I wanted the extra column to have the same data for each row
Where $syncData is an array of IDs:
$syncData = array_map(fn($locationSysid) => ['other_column' => 'foo'], array_flip($syncData));
or without arrow
$syncData = array_map(function($locationSysid) {
return ['ENTITY' => 'dbo.Cli_Core'];
}, array_flip($syncData));
(array_flip means we're using the IDs as the index for the array)