Tabs are a major user interface element in Safari—we use them all the time, but they become unwieldly and hard to manage. Apple hopes to address those problems in Safari 15 with a new tab implementation and features.
Here’s how tabs work in Safari 15 and how to make tab groups. If you want to try it out for yourself, you don’t have to wait for macOS Monterey—the Safari Technology Preview includes the new tabs, and it’s available for macOS Big Sur right now. (Note: the Preview has a version number of 14.2. Safari in macOS Monterey is version 15.)
Apple changed the way tabs are displayed in Safari 15. Previously, the new tab you created appeared below the Address/Search box and the Favorites Bar. Now tabs occupy the space of the Address/Search box, which allows a bit more of a webpage to show on the screen. A nice design touch in Safari 15 is that the toolbar can take on the color of a website. It’s a subtle way to let you know what site you are on, which can be helpful if you have several tabs open.
This new UI is on by default, but you do have the option to switch to a more familiar design, where the Address/Search box stays put in the middle and the tabs appear below it. Go to View > Show Separate Tab Bar and Safari will revert back.
Read more at MacWorld.com