Render partial in Stimulus.md

 fetch(href, {
      headers: {
        Accept: "text/vnd.turbo-stream.html",
      },
    })
      .then(r => r.text())
      .then(html => Turbo.renderStreamMessage(html))
//  optionally reflect the url    .then(_ => history.replaceState(history.state, "", href))

import { Controller } from '@hotwired/stimulus'

export default class extends Controller {
  static values = {
    src: String,
  }

  connect() {
    fetch(this.srcValue, {
      headers: {
        Accept: "text/vnd.turbo-stream.html",
      },
    }).then(r => r.text())
      .then(html => Turbo.renderStreamMessage(html))
  }
}

Link

import { Controller } from "@hotwired/stimulus"
import { FetchRequest } from '@rails/request.js'


export default class extends Controller {
  static targets = [ "formSelect", "dynamicForm" ]

  async fetch_dynamic() {
    let selection = this.formSelectTarget.value
    const request = new FetchRequest('get', '/posts/new', { query: {type: selection}})
    const response = await request.perform()
    if (response.ok) {
      const form = await response.text
      const dynamic_form = this.dynamicFormTarget
      dynamic_form.innerHTML=form
    }
  }
}

= form_for @post, html: {'data-controller'=>'form'} do |f|

  = f.label :workflow 
  = f.select :workflow, options_for_select(@workflow_options), {}, 'data-action'=>'change->form#fetch_dynamic', 'data-form-target'=>'formSelect', id: 'form_select'
  %div{'data-form-target'=>'dynamicForm'}
    = f.label :information, "Enter your information"
    = f.text_field :information
  %br
  = f.submit "Create Post"

class PostsController < ApplicationController

# GET /posts/new
def new
  @post = Post.new
  @workflow_options = %i[foo bar baz qux] # different form partials
  requested_form = params[:type] # type of form partial specified in a query parameter
  if requested_form
    render partial: "#{requested_form}_form", layout: false
    return
  end
end

end

#_baz_form.html.haml

= label :post, :information, "Enter your baz information"
= text_field :post, :information

async uploadFileToServer(file) {
  // ...
  const response = await fetch("/test/upload", {
    // ...
  })
  
  const html = await response.text()
  Turbo.renderStreamMessage(html)
}

Turbo.visit(url, { frame: '_top', action: 'advance' })