[MM-61969] Fix regression where search suggestion would break when using uppercase letters (#29400)

e2e-tests/playwright/tests/functional/channels/search/search_box_suggestions.spec.ts

@@ -0,0 +1,32 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {expect, test} from '@e2e-support/test_fixture';
+
+test('Search box suggestion must be case insensitive', async ({pw, pages}) => {
+    const {user} = await pw.initSetup();
+
+    // # Log in a user in new browser context
+    const {page} = await pw.testBrowser.login(user);
+
+    // # Visit a default channel page
+    const channelsPage = new pages.ChannelsPage(page);
+    await channelsPage.goto();
+    await channelsPage.toBeVisible();
+
+    // # Open the search UI
+    await channelsPage.globalHeader.openSearch();
+
+    const searchInput = await page.getByPlaceholder('Search messages');
+
+    // * it's working when using lowercase
+    await searchInput.fill('In:off');
+    await searchInput.press('Enter');
+    await expect(searchInput).toHaveValue('In:off-topic ');
+
+    // * it's working when using uppercase
+    await searchInput.clear();
+    await searchInput.fill('In:Off');
+    await searchInput.press('Enter');
+    await expect(searchInput).toHaveValue('In:off-topic ');
+});