How to render an ErrorView, without FallbackController?

You should check your log for the details.

But also setup your 500 error handler.

Ok, that’s fixed. My 2nd question remains.

You can build your own render error function if You want to dry your code.

def test1(conn, params) do
    case Repo.get_by(MyModel, title: params["title"]) do
      nil -> render_error(conn)
...

defp render_error(conn) do
  conn
  |> put_status(403)
  |> put_layout(false)
  |> render(MyAppWeb.ErrorView, "404.html")
end

What’s unclear?

How can render an error html template with no layout without having to say put_layout(false) from a controller? Namely, I want to set “nil” layout from within ErrorView.

No You can’t.