We recently updated our nuget reference for "Telerik.UI.for.AspNet.Core" to Version="2023.2.606", and the Select All checkbox stopped working. (It only selects the first row)
It works using Version="2020.2.617"
Here is one of our grids:
            <div class="table table-responsive" style="background-color:#444547">
                @(Html
                    .Kendo()
                    .Grid<ViewModelRedacted>()
                    .Name("grdUnitsList")
                    .Columns(columns =>
                    {
                        columns.Select().Width("20px");
                        columns.Bound(c => c.Id).Hidden(true);
                        columns.Bound(c => c.Name).Title(UnitsController.NameColumn);
                    })
                    .Selectable(s => s.Mode(GridSelectionMode.Multiple))
                    .ColumnMenu()
                    .ToolBar(tool => tool.Excel())
                    .Excel(ex => ex
                    .FileName("Units.xlsx")
                    .Filterable(true)
                    .AllPages(true)
                    )
                    .Navigatable()
                    //.Scrollable()
                    .Pageable()
                    .Filterable()
                    .Sortable(sortable =>
                    {
                        sortable.SortMode(GridSortMode.SingleColumn);
                    })
                    .Resizable(resize => resize.Columns(true))
                    .DataSource(dataSource => dataSource
                    .Ajax()
                    .PageSize(20)
                    .Model(model => model.Id(p => p.Id))
                    .ServerOperation(false)
                    .Read(read => read.Action("GetUnits", "Units"))
                    )
                    )
</div>