I second this feature request. It would be really useful. An implementation such as the one found here would be very nice:
Unfortunately that particular extension does not work on Opera GX so it would be greatly appreciated if it were to be natively implemented in Opera GX.
Essentially what the extension does is group the tabs by domain so say you have 7 different youtube tabs open. Firstly all 7 tabs would be grouped together in the top most tab selector in a tab called Youtube afterwards, once you click on it, a 2nd tab selector appears below the top one where u can select which one of the 7 tabs u wanna look at. It basically creates a top most main tab selector and a secondary tab selector below the top one for the tab currently selected.