Before making any changes, always create a full backup of your website, including both files and the database. This ensures that you can restore your site if anything goes wrong during the process.

Update Helix Ultimate to the Latest Version

Ensure you are using the latest version of Helix Ultimate before upgrading to Joomla 6.

• The most recent compatible version before the current one is v2.1.3.

You can update Helix Ultimate by following the usual process.

• Do not use Helix Ultimate v2.2.x for old Joomla versions, including J3.x series. 
• New template and plugin updates are not needed for Joomla 4 sites. It contains changes for Joomla 6 and PHP 8.4 only.

Disable “Behaviour - Backward Compatibility” Plugin

Joomla 6 requires this plugin to be disabled for Helix Ultimate to function properly.

1. Go to System > Plugins.
2. Search for "Behaviour - Backward Compatibility".
3. Unpublish or disable the plugin.

Verify Compatibility

Once Helix Ultimate is updated, and the plugin is disabled:

• Clear Joomla (5/6) cache, especially if you are using JCH Optimize or a similar "Speed up" extension.
• Refresh or clear the browser cache. 
• Check your site’s frontend to ensure everything displays correctly. It's always recommended to check the site on two different browsers.
• Verify that Helix Ultimate’s features (layout builder, menu, blog layout, etc.) work as expected.

Final Check

• Confirm your site is running Helix Ultimate v2.2.x.
• Ensure no error messages or layout issues appear.
• Optionally, check the browser console for any compatibility warnings. Or use Debug mode from Global Configuration. 

Your Helix Ultimate template should now be fully updated and compatible with Joomla 6.