Regex search on Date fields' string value

Hi I have few date fields in my index, all mapped to "type": "date"

Their values are like

"Created": "2021-12-13T23:07:36.421Z”

“Updated":  "2021-12-13T23:07:36.421z”

I want to search on the text value for those fields to get all the documents who has date fields’ end with ‘z’.

regexp does not work with date fields
I’ve also tried with “query_string”,

GET /_search
  "query": {
    "query_string": {
      "query": "/.*Z/",
      "fields": ["Updated"]

which did not hit anything.

Is there anyway i can do string search against all date fields?