If I specify "SortMode.Mixed" for a Grid's "SortMode" (via the .Sortable fluent method), the sort mode in the JavaScript initializer is set to "multiple" instead. This can even be seen on the MVC Demo page here: https://demos.telerik.com/aspnet-mvc/grid/sorting (the "mixed" demo behaves just like "multiple").

In the Kendo MVC source code for 2022.1.301, the GridSortableSettings.Serialize method appears to use the following logic:

if (SortMode != GridSortMode.SingleColumn)
{
    json["mode"] = "multiple";
}