How can I get the event while a page closes in Blazor Server side?

You can get the event using IDisposable interface to invoke the Dispose event on each page navigation or on closing a page. Find the code example for your reference.

@page "/"

@implements IDisposable;

<h1>Hello, world!</h1>

Welcome to your new app.

@code {

    public void Dispose()
    {

    }
}