Dolphin refuses to let users drag a toolbar to the left/right of a window when it has an address bar on it, which is completely sensible: horizontal-only things don't make sense on a vertical toolbar. However, Dolphin doesn't clearly communicate this to the user. When the user tries to drag a toolbar to an invalid place, it just silently doesn't do the thing and doesn't give any feedback at all.
In case some visual information is needed, in this Mastodon post you can find a video with the issue. https://mastodon.social/@DavidMarzalC/108589260335996462 Plasma 5.25.2 on Wayland, Dolphin 22.04.2