UX: Hide hamburger dropdown when `enable_sidebar` query param is used (#20367)

app/assets/javascripts/discourse/app/widgets/header.js

@@ -339,11 +339,7 @@ createWidget("header-icons", {
       },
     });
 
-    if (
-      this.siteSettings.navigation_menu === "legacy" ||
-      !attrs.sidebarEnabled ||
-      this.site.mobileView
-    ) {
+    if (!attrs.sidebarEnabled || this.site.mobileView) {
       icons.push(hamburger);
     }
 

spec/system/page_objects/components/sidebar.rb

@@ -7,6 +7,10 @@ module PageObjects
         page.has_css?("#d-sidebar")
       end
 
+      def not_visible?
+        page.has_no_css?("#d-sidebar")
+      end
+
       def has_category_section_link?(category)
         page.has_link?(category.name, class: "sidebar-section-link")
       end

spec/system/viewing_sidebar_spec.rb

@@ -17,6 +17,22 @@ describe "Viewing sidebar", type: :system, js: true do
 
       expect(sidebar).to be_visible
       expect(sidebar).to have_category_section_link(category_sidebar_section_link.linkable)
+      expect(page).not_to have_css(".hamburger-dropdown")
+    end
+  end
+
+  describe "when using the sidebar navigation menu" do
+    before { SiteSetting.navigation_menu = "sidebar" }
+
+    it "should not display the sidebar when `enable_sidebar` query param is '0'" do
+      sign_in(user)
+
+      visit("/latest?enable_sidebar=0")
+
+      sidebar = PageObjects::Components::Sidebar.new
+
+      expect(sidebar).to be_not_visible
+      expect(page).to have_css(".hamburger-dropdown")
     end
   end
 end