Turbo-iOS with ESM/importmaps?

I’m trying to run a turbo-ios with ESM/importmaps, specifically to do

import { Turbo } from "@hotwired/turbo-rails"
window.Turbo = Turbo

as per the docs, but didn’t succeed. Note that the above works when doing this via webpacker, it gives me back an actual Module as window.Turbo, while the ESM/importmaps version gives me a Javascript object (I think).

What I’ve tried:

# application layout
<%= javascript_include_tag "turbo", type: "module-shim" %>
<%= stimulus_include_tags %>

<script type="module-shim">
  import { Turbo } from "turbo"
  window.Turbo = Turbo  

# importmap
"imports": {
  "turbo": "<%= asset_path "turbo" %>",