Set the deletion_protection attribute to true.

Example Configuration

resource "google_compute_instance" "allowed" {
  name                = "test"
  machine_type        = "e2-medium"
  zone                = "us-central1-a"
  deletion_protection = "true"

  boot_disk {
    initialize_params {
      image = "debian-10-buster-v20220920"
    }
  }

  network_interface {
    network = "default"
  }
}