How I can remove a duplicate game in my collection

Go to My Collections in the top-right menu. When you hover with the mouse over a game, several commands appear, among which Remove.

In the hover menu does not appear remove option

I would also like to ask the same question.

Are you trying to right-click by any chance? Just bring the mouse cursor over the game. (You do need a mouse, not just a touchscreen.) Come to think of it, what browser do you have? It could be a compatibility issue...