Hi Ten Ho,
Thanks for visiting Microsoft Community.
The "Focus Cell" feature is indeed currently in Beta testing. However, its availability is still unstable, and Microsoft has not yet released any support articles about this new feature. You can do the following two things:
- Upgrade your Beta version of Office to the latest version (you can check the update history here Update History for Office Beta Channel - Office release notes | Microsoft Learn).
- Patiently wait for the feature to be fully available and for the official support articles to be released.
Thank you for your understanding.
Best Regards,
Jonathan Z - MSFT | Microsoft Community Support Specialist