Unable to create index in Elasticsearch 7.5.0

Elastic Stack Elasticsearch
5

I cant get kibana up and running because of this error. Hence I am using terminal to issue commands.

[elastic@my-linux-machine ~]$ curl -X PUT "http://my-linux-machine:9200/test?pretty"
{
  "error" : {
    "root_cause" : [
      {
        "type" : "mapper_parsing_exception",
        "reason" : "Root mapping definition has unsupported parameters:  [_all : {enabled=false}]"
      }
    ],
    "type" : "mapper_parsing_exception",
    "reason" : "Failed to parse mapping [_default_]: Root mapping definition has unsupported parameters:  [_all : {enabled=false}]",
    "caused_by" : {
      "type" : "mapper_parsing_exception",
      "reason" : "Root mapping definition has unsupported parameters:  [_all : {enabled=false}]"
    }
  },
  "status" : 400
}

As I outlined in my previously raised issue , all my indices have this

"mappings" : {
  "_all" : {
    "enabled" : false
  },
  "properties" : {
    "@timestamp" : {

I am not sure about the sequence of events and hence will not blame anyone. But the upgrade assistant did say all clear. Maybe I did not use it the right way.

My thinking is that presence of these indices with this _all in mapping is causing the ES 7 to act up.

I tried by closing all the existing indices. And then tried to create a sample index but of no avail.

I can extract the mapping of the existing indices via python client and remove the _all section from it. But it is not allowing me to put in an index with this updated mapping also. So option of reindexing the existing indices into new indices with correct mapping is also not available to me.