Hi Niels,
Greetings from Syncfusion support.
We have checked your reported problem with Sidebar component. We would like to let you know that, this(@inherits SampleBaseComponent) is local class reference used for our sample browser site. You no need to use this reference to render Sidebar (or any other SF Blazor components) in your application.
For your reference, we have prepared a sample for rendering the Sidebar component.
Refer the below links to know more about the Sidebar component.
Please let us know, if you need any further assistance.
Regards,
Sowmiya.P