Safari introduced “tab groups” a while back, which to me is an insane mess of complexity. When I think about it though they’re just folders and each tab is a bookmark/favorite.
The vertical tabs in Brave remind me of bookmarks/favorites too.
These are tabs that I don’t want to close as they have context and sometimes ongoing edits. It’s a bit like having multiple windows each with tabs but this keeps it together in one window and makes it easier to manager.
Without this, I would be facing 50-75 tabs and trying to figure out which ones were related to the project I needed to work on at the current time.
There are some others, but I haven't tried a wide range of them. Panorama does what I need.
As for tab groups, I could never get used to them, but I do use vertical tabs and find them quite useful.
What counts isn't some abstract storage concept but the UI and UX to manage them. Bookmarks are this drawer in your basement where you have to actively spend energy to find them. Tree tabs are self organizing. How they are are stored is irrelevant to me.
Arc has "pinned tabs", but not "bookmarks". While they can be used similarly, I find it quite annoying to use the search to pull something out of my "bookmarks", only to have it open a directory hierarchy eight levels deep when I switch to it.
Likewise, if I navigate away from the page on the pinned tab, I lose my "bookmark".