How to use output from one terraform resource for_each in another resource?

I'm new to Terraform and trying to figure out how to use it to create multiple VMs in different Azure regions. I'm expecting it to do the entire deployment, including creating VNETs, subnets, NICs, and everything related to the VM. I've gotten pretty far, but am stuck on how to get the subnet ID that gets created and use it in the NIC creation. I have tried a few different things and can't get it to work how I need it to. If there is a more efficient way to achieve this I'd love to hear it!

Here's my code:

variable "regions" {
    type = map(object({
        name = string
        region = string
        address_space = string
        }))
        default = {
            "us-east-2" = {
                name = "us-east-2"
                region = "East US 2"
                address_space = "10.1.0.0/16"
            },
            "uk-south" = {
                name = "uk-south"
                region = "UK South"
                address_space = "10.2.0.0/16"
            },
            "aus-east" = {
                name = "aus-east"
                region = "Australia East"
                address_space = "10.3.0.0/16"
            }
        }
}

variable "resource-group" {
    default = "rg-vm"
}


resource "azurerm_virtual_network" "vnet" {
    for_each = var.regions 

    name = "vnet-${each.value.name}"
    location = each.value.region
    resource_group_name = var.resource-group
    address_space = ["${each.value.address_space}"]
}

resource "azurerm_subnet" "subnet-lan" {
    for_each = var.regions

    name = "vnet-${each.value.name}-LAN"
    resource_group_name = var.resource-group
    virtual_network_name = "vnet-${each.value.name}"
    address_prefixes = ["${cidrsubnet(each.value.address_space, 8, 1)}"]
}

output "subnet_ids" {
    value = {
        for k, v in azurerm_subnet.subnet-lan : k => v.id
    }

    depends_on = [azurerm_subnet.subnet-lan]
}

resource "azurerm_network_interface" "nic" {
    for_each = var.regions

    name = "nic-${each.value.name}-ub-vm01"
    location = each.value.region 
    resource_group_name = var.resource-group

    ip_configuration {
      name = "ipconfig1"
      subnet_id = each.value.id
      private_ip_address_allocation = "Dynamic"
    }

}

I have tried using an output clause among other things and I keep getting errors when trying to reference the subnets that get created.

Using output from one terraform resource for_each in another resource

Issue seems to with the way you refer the each.value.id for azurerm_network_interface this refers won't add the actual ID which may results in the blocker.

Try refer as mentioned below make necessay changes as in the way you refering subnet in NIC as mentioned below

Demo configuration:

variable "regions" {
    type = map(object({
        name          = string
        region        = string
        address_space = string
    }))
    default = {
        "us-east-2" = {
            name          = "usvk-east-2"
            region        = "East US 2"
            address_space = "10.1.0.0/16"
        },
        "uk-south" = {
            name          = "ukvk-south"
            region        = "UK South"
            address_space = "10.2.0.0/16"
        },
        "aus-east" = {
            name          = "ausvk-east"
            region        = "Australia East"
            address_space = "10.3.0.0/16"
        }
    }
}

variable "resource_group_name" {
    default = "rgvk-vm"
}

resource "azurerm_resource_group" "rg" {
    name     = var.resource_group_name
    location = "East US"
}

resource "azurerm_virtual_network" "vnet" {
    for_each = var.regions

    name                = "vnet-${each.value.name}"
    location            = each.value.region
    resource_group_name = azurerm_resource_group.rg.name
    address_space       = [each.value.address_space]
}

resource "azurerm_subnet" "subnet" {
    for_each = var.regions

    name                 = "subnet-${each.value.name}"
    resource_group_name  = azurerm_resource_group.rg.name
    virtual_network_name = azurerm_virtual_network.vnet[each.key].name
    address_prefixes     = ["${cidrsubnet(each.value.address_space, 8, 1)}"]
}

resource "azurerm_network_interface" "nic" {
    for_each = var.regions

    name                = "nic-${each.value.name}-ub-vm01"
    location            = each.value.region
    resource_group_name = azurerm_resource_group.rg.name

    ip_configuration {
        name                          = "ipconfig1"
        subnet_id                     = azurerm_subnet.subnet[each.key].id
        private_ip_address_allocation = "Dynamic"
    }
}

deployment:

Refer:

https://build5nines.com/terraform-ip-functions-for-managing-ip-addresses-cidr-blocks-and-subnets/

https://discuss.hashicorp.com/t/multiple-for-each/51076

https://dev.azure.com/v-scheedella/MT%20Stack%20Overflow/_workitems/edit/42784