​Terraform 1.3.1 released, which means we are now safe to use 1.3.x, where optional() feature in variables is GA:

variable "with_optional_attribute" {
  type = object({
    a = string                # a required attribute
    b = optional(string)      # an optional attribute
    c = optional(number, 127) # an optional attribute with a default value
  })
}

More here - https://github.com/hashicorp/terraform/releases/tag/v1.3.0

#terraform