It could be something nice that resembles in a way the Workspaces (it is NOT the same thing but better than nothing).
The idea is to keep using Orizontal tabs (not vertical tabs), enablinh the sidebar inside of which you could see buttons that recall tab groups you have. A click on the Tab Group in the sidebar would open the group so in fact in the sidebar you'd only have the group name and cliccking on it would expand the tabs related to this group orizzontaly (as I said vertical tabs are disabled).
This could offer a clean view leaving the default Orizzontal Tabs but beeing able to switch to the Tab Groups by cliccking the Group reference in the sidebar