public MainVM()
{
    Task.Run(async () =>
    {
        await InitBooksCollectionAsync();
    });         


    InitCmds(); 
}

When in designer mode it executes the ViewModel constructor too.

While the designer process is sub process of Visual Stuido with limited resource, memory, lower render priority and is very easy to be blocked when loaded large data.

The solution is to judge desiger mode at first. Only not designer mode can load huge data