The grid's main element is a <div> and, as a block element, it takes 100% of its parent width. The table-layout property is fixed so the content does not stretch the columns.
Thus, the solution to set the grid width and scrolling, at least until we implement features for that, is to put it in a <div> that has the desired width.
You may also find interesting this request: https://feedback.telerik.com/blazor/1434744-hide-column-only-on-small-device.
UI for Blazor