What’s following your cursor? It’s not obvious in the image. Is it the lighting?
No, it’s the coloured lookalike rubix cube with the 4 spheres on top!
Try to press-depress left mouse click, right mouse click, middle mouse click while also pressing-depressing Ctrl, Shift, and Alt. That will reset your keyboard state. That happens sometimes to me too as if I’m dragging the object with Alt+mouse click when I’m just actually pressing Left-Click.
It’s not an object, that’s the thing, I have no idea what it is or how it appeared, but it doesn’t appear in-game. Looks like something related to materials but I have no idea what!
(Also I tried your suggestions, none worked!)