Centered taskbar app indicators work well on 16:9 and wider screens. On such screens, UI elements placed at corners are less prominent, you have to extort a deliberate effort to look there, unlike on tiny, 4:3 of yore. Ever since I got my ultrawide, and long before Windows 11 made this a default, I've been using bottom centered app buttons and Start/widget in the left corner. On a narrower and smaller screens (like a laptop), I find vertical taskbar more ergonomic, and centered/top aligned app buttons don't matter as much there in practice.