Unable to restore to an index in a newer Elastic Version

[mastersmit (Smit)]

I have taken a snapshot in the version 7.8 and uploaded to AWS S3. After which, I have downloaded a newer version of elastic 7.12 and configured AWS S3.

I am able to see the snapshots in kibana, and the restoring is also successful.

But the index is in yellow health with below stat:

{
  "_shards": {
    "total": 2,
    "successful": 0,
    "failed": 1,
    "failures": [
      {
        "shard": 0,
        "index": "elastic_snapshot_demo",
        "status": "INTERNAL_SERVER_ERROR",
        "reason": {
          "type": "unsupported_operation_exception",
          "reason": "_source only indices can't be searched or filtered"
        }
      }
    ]
  }
}

Also when trying index this: It is only showing this fields, but not my _source fields:

Also Mapping is correct though:

{
  "elastic_snapshot_demo" : {
    "mappings" : {
      "enabled" : false,
      "_meta" : {
        "_doc" : {
          "properties" : {
            "message" : {
              "type" : "text",
              "fields" : {
                "keyword" : {
                  "type" : "keyword",
                  "ignore_above" : 256
                }
              }
            },
            "user" : {
              "properties" : {
                "id" : {
                  "type" : "text",
                  "fields" : {
                    "keyword" : {
                      "type" : "keyword",
                      "ignore_above" : 256
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}