In issue #75180 there's a request for allowing Shift + mouse wheel to scroll widgets horizontally. I think that's a great addition but we should also have a mechanism in Flutter to let us decide if we want Shift + mouse wheel or just mouse wheel for horizontal scroll.

Shift + mouse wheel is specially helpful if the screen can scroll both vertically and horizontally at the same time (like in a web browser or a spreadsheet), but when only one is possible, then I have seen both behaviors in desktop apps.

I see some reasons for this:

1. Flutter is loved for being highly customizable, so if we lock one keyboard + mouse combination for horizontal scroll, then Flutter won't give the developers the ability to customize their apps as much as they want.

2. Shift + mouse wheel forces the user to use both hands (one in the keyboard and another in the mouse), but in some applications this isn't desired. Imagine a Financial Advisor calling their clients to give a stock recommendation, while they look at an horizontally scrolling list of stocks. How can he hold the phone, talk, press Shift and scroll the mouse. This can be cumbersome.

3. People with disabilities can have a hard time holding shift and scrolling at the same time.

4. I have seen desktop apps that scroll horizontal lists with just the mouse wheel, so porting them to Flutter would break the user experience. Firefox is a great example, when we have many tabs we can scroll them with the mouse wheel without pressing Shift.

Here's one example of user interfaces where people would want to scroll a list horizontally, with just the mouse wheel. A desktop trading terminal, with an horizontal, animated, stock ticker list (pointed by the red arrow, inside the red rectangle), that continuously scrolls to the left (and the user can also scroll it with the mouse, in order to make it scroll faster or go backwards):