On Wayland, if user clicks to activate a window in the tooltip, then opens the tooltip again, the ToolTipWindowMouseArea still thinks the thumbnail is being hovered is true, so the highlight is displayed again even though the mouse isn't actually hovering over the thumbnail, just over the icon. I have an MR which adds a workaround for this, but the root cause should be investigated at some point. https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/494
It's working fine here. Can you please test on 5.23 beta (or master)?
*** This bug has been marked as a duplicate of bug 427572 ***