The values of system fields on the custom metadata object are only available via Tooling API. In the ontology of entities covered by Tooling API, you will not find a Custom Metadata entity. This is so because underneath the hood the custom metadata object is represented as a...custom object.  Full list of system fields is [documented](https://developer.salesforce.com/docs/atlas.en-us.api_tooling.meta/api_tooling/tooling_system_fields.htm); some of these fields aren't shown on the custom metadata type object definition screen.

The easiest way to grab this data from Tooling API is via REST using the `query` resource. To do so, you need to know the Object Name of custom metadata type. The value of Object Name can then be used to compose a `DeveloperName` predicate in a query against `CustomObject` entity:
```
/services/data/v49.0/tooling/query/?q=SELECT+Id,CreatedById,CreatedDate,LastModifiedById,LastModifiedDate+FROM+CustomObject+WHERE+DeveloperName='Truck_Configurations'
```

Response with redacted values:

```
{
  "size" : 1,
  "totalSize" : 1,
  "done" : true,
  "queryLocator" : null,
  "entityTypeName" : "CustomObject",
  "records" : [ {
    "attributes" : {
      "type" : "CustomObject",
      "url" : "/services/data/v49.0/tooling/sobjects/CustomObject/01I..."
    },
    "Id" : "01I...",
    "CreatedById" : "005...",
    "CreatedDate" : "...",
    "LastModifiedById" : "005...",
    "LastModifiedDate" : "..."
  } ]
}
```