Opera used to be a fantastic web browser, with a custom high-performance Presto rendering engine and features like tabbed windows that didn't show up in competing browsers until years later. However, the modern Opera browser is a shadow of its former self, reliant on chasing trends and meme advertis...
Fair, that is pretty awesome feature, especially for the tab sprawl in this day and age.
I (obviously) use Firefox, and I had the same problem, and found the "Tree Style Tab" extension solves the same problem for me, however it does it in a very different way.
Instead of having your tabs along the top of the window, your tabs are kept in a sidebar, and vertically. Opening new tabs from an already open page makes the new tabs nest under the original tab. You can collapse and expand whole trees of tabs, and move them around should you need to.
It also integrates nicely with the "Container Tabs" putting a colored band next to the tabs belonging to each container.
The tabs being vertical also means that you can always read the titles of the tabs, they don't get "squished".
It does cost a chunk of screen real estate, but for me the organization is worth it.
That tree tabs sounds awesome. I'm using container tabs already and it's greatly helped my tabs become less of a mess. But keeping them organized based on which tab I spawned them from sounds great, too. And tbh, it not hiding the original tab bar sounds even better because then I can combine the organization of container tabs with the historical origin of the tabs from tree style tabs and just use whichever one feels more intuitive in the moment to find the tab I'm looking for (or to traverse open tabs for cleanup).
I just want to mention that there is a lot of configuration options in Tree Style Tab, so if it doesn't behave exactly how you want it to, there's a high likelihood that you just need to tweak the settings a bit.