This release update has been postponed indefinitely and not enforced in its present form. Don’t enable it.
Where: This change applies to Lightning Experience in Essentials, Professional, Enterprise, Performance, Unlimited, and Developer editions. Lightning console apps are available for an extra cost to users with Salesforce Platform user licenses for certain products. Some restrictions apply. For pricing details, contact your Salesforce account executive.
When: This update has been postponed indefinitely.
Keep Working with Tab-Focused Dialogs (Release Update) (salesforce.com)