To add the horizontal scrollbar to the datagrid you could add the following CSS to your custom.css stylesheet, and add the class 'scroll-horizontal' to the datagrid where you want to apply the horizontal scrollbar. This will keep the positioning of the search fields, control bar, and paging buttons.
.scroll-horizontal .mx-grid-content {
overflow-x: scroll;
}
.scroll-horizontal .mx-datagrid-content-wrapper {
width: 2000px;
}
It is possible when you style deeper in the Mendix structure.
In example: give the mx-grid-content the scroll overflow. and give mx-templategrid-content-wrapper (which is a few levels deeper) a max-width and width.