The request is the compact tabs themselves where the search bar becomes a part of the tab. Otherwise it would have been titled "Vertical tab space." Although I named it precisely as such, users may have upvoted it in support of either the vertical tab space-saving or the radical Safari 15 compact tabs. Although there has been major backlash against the Safari 15 design and Apple reverted back disappointingly.
It seems to be roughly 2:1 ratio of Safari 15 tab's design against vertical tab saving from my counting, because I do not know the current views of the users who have upvoted this post on whether they seem to be in support of the shortened vertical height or the design of Safari 15's tab toolbar itself. Perhaps a community poll would be better than a single-dimensional constant.
Edit: I did not articulate enough, but it's not that the address bar is embedded within the tab bar, but rather that you can see multiple tabs while still having only a one-row toolbar.