public IAccordionItemInfo GetSelectedItemInfo()

<DxAccordion @ref=MyAccordion 
             SelectionMode="NavigationSelectionMode.Single" 
             SelectionChanged="@OnSelectionChanged">
    <Items>
        <DxAccordionItem Text="Shapes">
            <Items>
                <DxAccordionItem Text="Circle" />
                <DxAccordionItem Text="Square" />
            </Items>
        </DxAccordionItem>
        <DxAccordionItem Text="Templates" />
    </Items>
</DxAccordion>

@code {
    DxAccordion MyAccordion;
    void OnSelectionChanged(AccordionSelectionChangedEventArgs e) {
        MyAccordion.CollapseAll();
        MyAccordion.ExpandToItem((x) => x == e.SelectedItems.FirstOrDefault());
        if (MyAccordion.GetSelectedItemInfo().HasChildren) {
            MyAccordion.SetItemExpanded((x => x.Text == e.SelectedItems.FirstOrDefault()?.Text), true);
        }
    }
}