Can you fix your game Blizzard? This has been broken since 2010. (Before I was even playing) @mouseover, when bound to a mouse button, simply doesn’t work on unit frames, and only with mouseover for enemy or friendly models.
I remap my mouse buttons to keys in the mouse software (or MS Powertoys if mouse software doesn’t let you) and it solves this issue.
My mouse button 4 and 5 won’t work even as a hard target cast if my cursor is over a raid frame.
Might rebind them like the person above recommended, it’s a pain not being able to use those buttons for important abilities.
I ended up rebinding as F1 and F2.
I use MB4 for my mounts and MB5 for stuns.