macOS Catalina will take a few more weeks to appear as the final version for all users, but Apple has already released one of its novelties as an update: the new safari. Version 15 of this browser can now be downloaded and used on macOS Big Sur and macOS Catalina.
Tab groups are coming to all modern Macs
The main novelty of this version of Safari is a new design that simplifies the distribution of tabs in the upper area of the window, and also classifies them into groups so as not to lose control. When the interface was shown at WWDC and in subsequent betas it caused some controversy, so Apple has put an option to reverse the design to all users.
You can find this option in the browser preferences (menu Safari > preferences), in the section Tabs:
Regardless of the design you choose, the new function to group tabs remains active. As time passes we will see which arrangement of tabs is the one that triumphs. We could be facing a definitive design change in the making, or another experiment such as that of the upper tabs of Safari 4 that years ago ended up being withdrawn.
You can update to Safari 15 through System Preferences, in the panel Software update. Remember that this version of Safari will not appear as available in macOS Mojave and earlier versions of the system. To apply the update it is not necessary to restart the computer.