All credits go to How to debug Terraform variable content using this custom module, this is just a note to copy & past to my projects

resource "null_resource" "terraform_debug" {
    provisioner "local-exec" {
        command = "echo $VARIABLE1 >> debug.txt"
        environment = {
            VARIABLE1 = jsonencode(var.example)
        }
    }
}

Remove from state to be re-generated again

terraform state rm null_resource.terraform_debug

Big gotcha… just happen when do a terraform apply