If you start using Focus and it's not blocking distractions like it should, you might need to check your "Automation Permissions."
When you first open Focus, it will ask you to turn on something called Automation permissions.
Focus will prompt for permission to control a browser, click "OK" to allow
If you don't say OK to this, you can turn it on yourself. Just go to System Preferences > Privacy & Security > Automation. Then, make sure all the internet browsers are turned on under Focus:
You can check Focus has permissions by visiting System Preferences > Privacy & Security > Automation and enabling them if needed.
After that, close Focus and open it again. Start a new Focus time, and you'll see it's doing its job—keeping those distractions away.