@rosalaun Same here on Linux, there is no more opera://flags/#fast-tab-tooltip
which is how it used to work.
It's not great UI -- didn't need it, don't use it, sometimes it hangs around and you have to hover here and there for it to go away, takes up half the laptop screen. Not loving it.
There is an option to disable some of it, so that it doesn't cover up the video you're watching and stuff, in Settings / Advanced / User Interface / "Show tabs from the same domain in tab tooltip".