You can check the sample application attached to this thread. It shows what to do in order to avoid this behavior. Sidebar not working in .NET 8 RC1 experiment - #13 by korchev
<RadzenHeader style="position: static">
<RadzenStack Orientation="Orientation.Horizontal" AlignItems="AlignItems.Center" Gap="0">
<RadzenSidebarToggle @rendermode="@RenderMode.InteractiveServer" Click="@(() => sidebar1Expanded = !sidebar1Expanded)" />
<RadzenLabel Text="Header" />
</RadzenStack>
</RadzenHeader>
<RadzenSidebar Style="width:auto">