Hello,
so I have tab groups that I like to have open, but don't use in my daily life, I use them specifically, maybe daily, but just once at a specific time, for a particular reason, so when comes times to switch tabs by dragging horizontally the bottom of the screen, I would rather they don't show-up in there, so I can keep focused on what I'm doing.
In my opinion, you could achieve this several ways which could improve the overall experience in other ways at the same time, and boast brave, new features as is the Opera way.
I think you could create "pinned tabs", and tab groups, with a toggle "exclude pinned/unpinned tabs from horizontal scrolling", or better yet, workspaces on mobile, where you can switch vertically, and horizontally from the tab/group switching view (the tabs button second from the right on the bottom), such that you can drag the cards layout up, or down, and thus change the "workspace". For list view, this can simply be horizontal scrolling.
Under the hood, this is pretty simple to implement, In going to stick to cards for simplicity, I think you could just add a new property to tabs to tag the new row dimension, and in UI, you simply display those new rows as "workspaces", maybe with the ability to write a title for it, that's just a matter of tracking a new customizable UI element in a database (id, index, name), and performance-wise, there's no difference to having multiple tabs open. If it's found that this new scheme facilitates having too many tabs open for comfort hardware-wise, caps could be put in place dimensionally, and/or memory management/garbage collection that already exists could be enforced like closing old tabs, unloading tabs, only keeping so many tabs in RAM, etc...
As you can see, it's really not a far stretch, there's no need to have a dedicated button, or function like on desktop, and unless a patent exists, I really don't see why this feature shouldn't be implemented at once, and even if it does, I really don't think something as general as "row navigation" could be enforced.
Best regards,