Terraform import: invalid index

I'm trying to replace deprecated resource 'azurerm_sql_server' with the 'azurerm_mssql_server' and got an 'invalid index' error in the case.

A simplified demo of the situation (with Terraform v0.14.5 and v1.0.5):

terraform {
  required_providers {
    azurerm = {
      source  = "hashicorp/azurerm"
      version = "=2.49.0"
    }
  }
}

provider "azurerm" {
  features {}
}

locals {
  prefix = toset(["primary", "secondary"])
}

resource "azurerm_resource_group" "rg" {
  name     = "rgtest"
  location = "Canada Central"
}

resource "random_password" "sql_admin_password" {
  length      = 16
  special     = true
  number      = true
  upper       = true
  lower       = true
  min_special = 2
  min_numeric = 2
  min_upper   = 2
  min_lower   = 2
}

resource "azurerm_sql_server" "instance" {
  for_each = local.prefix

  name                = "${each.value}-sqlsvr"
  location            = azurerm_resource_group.rg.location
  resource_group_name = azurerm_resource_group.rg.name

  version                      = "12.0"
  administrator_login          = "ssadmin"
  administrator_login_password = random_password.sql_admin_password.result
}

locals {
  primary_sql_srv   = azurerm_sql_server.instance["primary"].name
  secondary_sql_srv = azurerm_sql_server.instance["secondary"].name
}

# other TF resources using local.primary_sql_srv and local.secondary_sql_srv

The infrastructure has been deployed and no intention to re-create the database servers so we need to change the resource and import existing servers. According to Terraform document, this can be done with 'terraform state rm' and 'terraform import' command.

So,

1. Change the configuration script

...

resource "azurerm_mssql_server" "instance" {
...
locals {
  primary_sql_srv   = azurerm_mssql_server.instance["primary"].name
  secondary_sql_srv = azurerm_mssql_server.instance["secondary"].name
}
# other TF resources using local.primary_sql_srv and local.secondary_sql_srv

2. Remove azurerm_sql_server resource from the state file, both are successful

terraform.exe state rm azurerm_sql_server.instance[`\`"primary`\`"]
terraform.exe state rm azurerm_sql_server.instance[`\`"secondary`\`"]

3. Import the primary database server

> terraform.exe import azurerm_mssql_server.instance[`\`"primary`\`"] "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/primary-sqlsvr"

azurerm_mssql_server.instance["primary"]: Importing from ID "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/primary-sqlsvr"...
azurerm_mssql_server.instance["primary"]: Import prepared!
  Prepared azurerm_mssql_server for import
azurerm_mssql_server.instance["primary"]: Refreshing state... [id=/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/primary-sqlsvr]

Import successful!

The resources that were imported are shown above. These resources are now in
your Terraform state and will henceforth be managed by Terraform.

Current state list

❯ terraform.exe state list

azurerm_mssql_server.instance["primary"]
azurerm_resource_group.rg
random_password.sql_admin_password

4. Import the secondary database server

> terraform.exe import azurerm_mssql_server.instance[`\`"secondary`\`"] "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/secondary-sqlsvr"

azurerm_mssql_server.instance["secondary"]: Importing from ID "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/secondary-sqlsvr"...
azurerm_mssql_server.instance["secondary"]: Import prepared!
  Prepared azurerm_mssql_server for import
azurerm_mssql_server.instance["secondary"]: Refreshing state... [id=/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rgtest/providers/Microsoft.Sql/servers/secondary-sqlsvr]

Error: Invalid index

  on C:\Work\Projects\2021\20210812RenameResource\t1env\main.tf line 49, in locals:
  49:   secondary_sql_srv = azurerm_mssql_server.instance["secondary"].name
    |----------------
    | azurerm_mssql_server.instance is object with 1 attribute "primary"

The given key does not identify an element in this collection value.

The state refresh for the 2nd import hit the locals block and failed due to no 'secondary' server resource.

So to me, this is a deadlock, I cannot import the 'secondary' server resource because of the refresh error and the refresh error was caused by the lack of the 'secondary' server resource.

Two ways I can think of:

1. Manually add the 'secondary' server resource to the state file, which is definitely not proper
2. Remove the 'locals' block which is OK in the demo but lots of changes in real code for dependencies.

Any thoughts, please? Thank you.