@pavelopdev Yeah the old multi document interface of the old Opera with each tab in their own mini window inside the main one was great. I'd really love to see a browser implement a MDI design like that again though I doubt it will happen any time soon, Vivaldi does have page tiling which is handy but it's not the same.
Hopefully since Chromium has added collapsible tab groups though it will make its way into Opera soon, though after some testing their implementation still needs quite a bit of work as you cannot use a tab while its collapsed so you need the group expanded which kinda kills the part of the reason to use tab groups.
@andrew84 Wow didn't know Edge implemented vertical tabs, just checked it out now on the dev build and it still needs a bit of work too such as being able to customise the width of the tab panel or changing position to the right instead of left. Still it's great to see another browser adding native vertical tabs, it's been a killer feature for me since I switched to Opera as my main browser back in 2007 and then Vivaldi since 2017 (after Opera stupidly changing the delayed loading behaviour of tabs by removing the ability to only load when activated). With Edge making the feature more mainstream it will be interesting to see if other browsers will implement their own vertical tabs.
For the tab grouping they are indeed using the Chromium solution which like I said above it also needs a bit of work still, but it's a start and will hopefully find its way into Opera soon too.