Does Vivaldi nest tabs yet? Its been a few years since I tried it but it didn't use to.
With TST, I can open a link as a new tab (middle click) and it is shown as a child of the opening tab. This makes it easy to minimise or close a whole tree of tabs.
>>aemble+(OP)
you can stack tabs in a group, and when you're inside that group, new tabs are opened within that group, but not sure about the middle click for a single tab
It also has a great alternative - workspaces, that helped me much better vs. the stacking, that for some reason didn't stick