I’d love to have in Brave the two level tab groups of Vivaldi, and I have tried to achieve that.
I installed on Windows 10 an app called Groupy (from Stardock) that add tabs support to all applications. Then I configured Groupy to handle Brave windows.
Just to test it I’ve created three Brave windows, and used Groupy to “convert” them to tabs.
It works, but it’s not optimal: I have three Brave processes, and I have to remember to exit brave using the “exit” menu. Also it’s not very fast in switching between groups.
I believe that it’s necessary to implement tab groups natively, so I’ll have to wait for Brave developers to add support for it.
link to video: