Enable or Disable Multi-picklist Field rendered as checkboxes

The Portal allows you to lock a row if it was already checked in the back-end. Use the enableRecord and enableSelectAll configurations for Multi-picklist Field rendered as checkboxes, so that a record that is selected previously can be disabled based on that condition.

"appearance": {
    "multipleSelections": true,
    "multipleSelectionOptions": {
      "renderSelectAll": true,
      "renderRecord": true,
      "enableRecord": "not($global.attr(previouslySelectedIds).contains($this.attr(id);",
      "enableSelectAll": true
    }
  }

Where, previouslySelectedIds is an array of strings that should be declared on a global value.