Support for Entity Type User and OG Membership

You need to use the machine name of the Drupal 7 entity type and bundle. All entities should be supported. Try:

$settings['migrate_skip_fields_by_name'] = [
  'user:user:field_name',
  'og_membership:*:*'
];

It is not feasible to include all entity types in the example settings. If the above does not work, add a new comment with your the value for migrate_skip_fields_by_name setting. Note that as of the latest release, a new required migrate_skip_fields_source_version should be used.