You can. Ctrl + Shift + B if you’re on Windows/Linux or ⌘ + Option + b on Mac.
This also exists. It’s called a sidebar. Go to brave://settings/appearance and you’ll see an option that says Show Sidebar. You just set it to On Mouseover and it will stay hidden until you move your mouse to the side. Then you click Bookmarks and the specific bookmark you want. It navigates to the page, you hit the little Bookmark icon on that and it vanishes.
They are actually working on improving it and there are some side panel flags that can be enabled in brave://flags, but I don’t specifically know what they do.
They actually have vertical tabs released in current Nightly version. Constant updates and modifications will be coming. So if this aspect won’t be, it should be added down the road.
So yeah, there you go. I know I shared link to extension as you asked in your topic. Then as you brought this up, I was finally able to see it and answer a bit. Though feel bad as OP hasn’t been around lately. This was from January. Then they posted in May about another issue, neither of them had responses from anyone. Not sure how they flew under the radar.