openapi distinct get and post items

Question

I have openapi requirements

   components:
     schemas:
       UserGet:
          allOf:
            - $ref: '#/components/schemas/myElements'
       UserPost:
          allOf:
            - $ref: '#/components/schemas/myElements'

       myElements:
         type: array
         items:
           allOf:
             - $ref: 'myEnumItems'

       myEnumItems:
          type: String
          enum:
             - 'state1'
             - 'state2'

UserGet and UserPost using myElements schema.

Problem is myElements have myEnumItems with enum state1 and state2, which I want to restrict new user can POST only any of two values ['state1','state2'], but in GET request there may be already available data in db for existing users for example 'state3'. Since 'state3' is not in enum, for GET this use case will fail.

I am looking for idea to overcome this issue.

I am using https://swagger.io/docs/specification/paths-and-operations/ as reference.

It looks similar to Re-using model with different required properties but readOnly is not working for me. I am not sure which part I am missing.