diff --git a/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.hbs b/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.hbs
index 915400a137b..8a158491509 100644
--- a/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.hbs
+++ b/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.hbs
@@ -3,69 +3,42 @@
   @class="sidebar-categories-form-modal"
 >
   <form class="sidebar-categories-form">
-    {{#each this.siteCategories as |category|}}
+    {{#each this.categoryGroupings as |categories|}}
       <div
         class="sidebar-categories-form__row"
-        style={{html-safe (border-color category.color "left")}}
+        style={{html-safe (border-color categories.1.color "left")}}
       >
-        <div
-          class="sidebar-categories-form__category-row"
-          data-category-id={{category.id}}
-        >
-          <label
-            class="sidebar-categories-form__category-label"
-            for={{concat "sidebar-categories-form__input--" category.id}}
+
+        {{#each categories as |category|}}
+          <div
+            class="sidebar-categories-form__category-row"
+            data-category-id={{category.id}}
+            data-category-level={{category.level}}
           >
-            <div
-              class="sidebar-categories-form__category-badge sidebar-categories-form__category-badge--parent-category"
+            <label
+              class="sidebar-categories-form__category-label"
+              for={{concat "sidebar-categories-form__input--" category.id}}
             >
-              {{category-badge category}}
-            </div>
+              <div class="sidebar-categories-form__category-badge">
+                {{category-badge category}}
+              </div>
 
-            <div class="sidebar-categories-form__category-description">
-              {{dir-span category.description_excerpt htmlSafe="true"}}
-            </div>
-          </label>
-
-          <Input
-            id={{concat "sidebar-categories-form__input--" category.id}}
-            class="sidebar-categories-form__input"
-            @type="checkbox"
-            @checked={{includes this.selectedSidebarCategoryIds category.id}}
-            {{on "click" (action "toggleCategory" category.id)}}
-          />
-        </div>
-
-        {{#if (gt category.subcategories.length 0)}}
-          {{#each category.subcategories as |subcategory|}}
-            <div
-              class="sidebar-categories-form__category-row"
-              data-category-id={{subcategory.id}}
-            >
-              <label
-                class="sidebar-categories-form__category-label"
-                for={{concat "sidebar-categories-form__input--" subcategory.id}}
-              >
-                <div
-                  class="sidebar-categories-form__category-badge sidebar-categories-form__category-badge--subcategory"
-                >
-                  {{category-badge subcategory}}
+              {{#unless category.parentCategory}}
+                <div class="sidebar-categories-form__category-description">
+                  {{dir-span category.description_excerpt htmlSafe="true"}}
                 </div>
-              </label>
+              {{/unless}}
+            </label>
 
-              <Input
-                id={{concat "sidebar-categories-form__input--" subcategory.id}}
-                class="sidebar-categories-form__input"
-                @type="checkbox"
-                @checked={{includes
-                  this.selectedSidebarCategoryIds
-                  subcategory.id
-                }}
-                {{on "click" (action "toggleCategory" subcategory.id)}}
-              />
-            </div>
-          {{/each}}
-        {{/if}}
+            <Input
+              id={{concat "sidebar-categories-form__input--" category.id}}
+              class="sidebar-categories-form__input"
+              @type="checkbox"
+              @checked={{includes this.selectedSidebarCategoryIds category.id}}
+              {{on "click" (action "toggleCategory" category.id)}}
+            />
+          </div>
+        {{/each}}
       </div>
     {{/each}}
   </form>
diff --git a/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.js b/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.js
index bfcd7837e35..b846be7bd75 100644
--- a/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.js
+++ b/app/assets/javascripts/discourse/app/components/sidebar/categories-form-modal.js
@@ -13,9 +13,30 @@ export default class extends Component {
     ...this.currentUser.sidebar_category_ids,
   ];
 
-  @tracked siteCategories = this.site.categoriesList.filter((category) => {
-    return !category.parent_category_id && !category.isUncategorizedCategory;
-  });
+  categoryGroupings = [];
+
+  constructor() {
+    super(...arguments);
+
+    this.site.sortedCategories.reduce(
+      (categoryGrouping, category, index, arr) => {
+        if (category.isUncategorizedCategory) {
+          return categoryGrouping;
+        }
+
+        categoryGrouping.push(category);
+
+        const nextCategory = arr[index + 1];
+        if (!nextCategory || nextCategory.level === 0) {
+          this.categoryGroupings.push(categoryGrouping);
+          return [];
+        }
+
+        return categoryGrouping;
+      },
+      []
+    );
+  }
 
   @action
   toggleCategory(categoryId) {
diff --git a/app/assets/javascripts/discourse/app/models/category.js b/app/assets/javascripts/discourse/app/models/category.js
index ba517c0b0de..5101056328d 100644
--- a/app/assets/javascripts/discourse/app/models/category.js
+++ b/app/assets/javascripts/discourse/app/models/category.js
@@ -70,7 +70,11 @@ const Category = RestModel.extend({
 
   @discourseComputed("parentCategory.level")
   level(parentLevel) {
-    return (parentLevel || -1) + 1;
+    if (!parentLevel) {
+      return parentLevel === 0 ? 1 : 0;
+    } else {
+      return parentLevel + 1;
+    }
   },
 
   @discourseComputed("subcategories")
diff --git a/app/assets/stylesheets/common/components/sidebar-categories-form.scss b/app/assets/stylesheets/common/components/sidebar-categories-form.scss
index 2ccfbf408b7..db31e1f49a6 100644
--- a/app/assets/stylesheets/common/components/sidebar-categories-form.scss
+++ b/app/assets/stylesheets/common/components/sidebar-categories-form.scss
@@ -21,22 +21,23 @@
     padding: 0.5em 0;
   }
 
-  .sidebar-categories-form__category-row:not(:first-child) {
-    border-top: 1px solid var(--primary-low);
-
-    .sidebar-categories-form__input {
-      align-self: center;
-    }
+  .sidebar-categories-form__category-row[data-category-level="0"] {
+    border-bottom: 1px solid var(--primary-low);
   }
 
-  .sidebar-categories-form__category-row:nth-child(2) {
-    padding-left: 1em;
-  }
-
-  .sidebar-categories-form__category-row:nth-child(n + 3) {
+  .sidebar-categories-form__category-row[data-category-level="1"] {
     margin-left: 1em;
   }
 
+  .sidebar-categories-form__category-row[data-category-level="1"]:not(:nth-of-type(2)) {
+    border-top: 1px solid var(--primary-low);
+  }
+
+  .sidebar-categories-form__category-row[data-category-level="2"] {
+    margin-left: 2em;
+    border-top: 1px solid var(--primary-low);
+  }
+
   .sidebar-categories-form__category-label {
     display: flex;
     flex-direction: column;
diff --git a/spec/system/editing_sidebar_categories_navigation_spec.rb b/spec/system/editing_sidebar_categories_navigation_spec.rb
index 6b5cd01cb24..fe1a74c896a 100644
--- a/spec/system/editing_sidebar_categories_navigation_spec.rb
+++ b/spec/system/editing_sidebar_categories_navigation_spec.rb
@@ -53,4 +53,39 @@ RSpec.describe "Editing sidebar categories navigation", type: :system do
     expect(sidebar).to have_no_section_link(category_subcategory2.name)
     expect(sidebar).to have_no_section_link(category2.name)
   end
+
+  describe "when max_category_nesting has been set to 3" do
+    before { SiteSetting.max_category_nesting = 3 }
+
+    it "allows a user to edit sub-subcategories to be included in the sidebar categories section" do
+      category_subcategory_subcategory =
+        Fabricate(:category, parent_category_id: category_subcategory.id)
+
+      category_subcategory_subcategory2 =
+        Fabricate(:category, parent_category_id: category_subcategory.id)
+
+      category2_subcategory_subcategory =
+        Fabricate(:category, parent_category_id: category2_subcategory.id)
+
+      visit "/latest"
+
+      expect(sidebar).to have_categories_section
+
+      modal = sidebar.click_edit_categories_button
+
+      expect(modal).to have_right_title(I18n.t("js.sidebar.categories_form.title"))
+
+      modal
+        .toggle_category_checkbox(category_subcategory_subcategory)
+        .toggle_category_checkbox(category_subcategory_subcategory2)
+        .toggle_category_checkbox(category2_subcategory_subcategory)
+        .save
+
+      expect(modal).to be_closed
+
+      expect(sidebar).to have_section_link(category_subcategory_subcategory.name)
+      expect(sidebar).to have_section_link(category_subcategory_subcategory2.name)
+      expect(sidebar).to have_section_link(category2_subcategory_subcategory.name)
+    end
+  end
 end