Why is json serialization generating errors when calling WebAPI?

To demonstrate the issue, I've added a few POST methods to the solution created by the Blazor WASM solution template. Some work, some don't, generating errors which I don't understand and I'm hoping someone out there can educate me.

Here's the client side code:

protected override async Task OnInitializedAsync()
{
    try
    {
        // From the Blazor template
        forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>("WeatherForecast");

        var w = new WeatherForecast();
        // Works
        await Http.PostAsJsonAsync<WeatherForecast>("WeatherForecast", w);
        
        MemoryStream s = new MemoryStream();
        // Generates exception: 'Timeouts are not supported on this stream.'
        await Http.PostAsJsonAsync<MemoryStream>($"WeatherForecast/stream", s);
        
        List<MemoryStream> l = new List<MemoryStream>() { new MemoryStream() };
        // Generates exception: 'Timeouts are not supported on this stream.'
        await Http.PostAsJsonAsync<List<MemoryStream>>($"WeatherForecast/list", l);
        
        List<MemoryStream> m = new List<MemoryStream>();
        // Works
        await Http.PostAsJsonAsync<List<MemoryStream>>($"WeatherForecast/list", m);
        
        // PdfDocument is part of the PdfSharp library which I'm using to build pdf
        // files but I need to send it into the API to save it on a server.
        PdfDocument doc = new PdfDocument();
        // Generates exception: 'System.Security.Cryptography.Algorithms is not
        // supported on this platform.'
        await Http.PostAsJsonAsync<PdfDocument>("WeatherForecas/pdf", doc);
    }
    catch (Exception e)
    {
        throw;
    }
}

Here's the server side API code:

    [HttpPost]
    public void Post([FromBody] WeatherForecast w)
    {
        if (w == null) return;

    }

    [HttpPost("stream")]
    public void Post([FromBody] MemoryStream s)
    {
        if (s == null) return;

    }

    [HttpPost("list")]
    public void Post([FromBody] List<MemoryStream> s)
    {
        if (s == null) return;

    }

    [HttpPost("pdf")]
    public void Post([FromBody] PdfDocument doc)
    {
        if (doc == null) return;

    }
}

The comments show which calls work and which ones don't, and for the ones that don't, the errors don't make sense to me. Can anyone help me understand why I can't send a PdfDocument to an API?

Thanks in advance for your help.