Rotating Slanted 3D Object Toward Mouse on Z Axis

Issue:

I’m currently working on a game, and I’ve got this issue with rotating a 3D object. The camera is initially rotated at -30 on the X axis, giving the object as a slight slant. I’m trying to make the object rotate towards the mouse on the Z axis, but the rotation behaves strangely and I’m having difficulty getting it to work properly.

Any advice or guidance would be greatly appreciated. I’m happy to explain or provide more screenshots if necessary.

Screenshots:
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What I’d like to happen:
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