Why do json dump looks cut off

You are dumping out the WebResponse which includes details of the content but not the actual content itself and you still need to read it using something like

using (var reader = new StreamReader(response.Content.ReadAsStream()))
{
    string json = reader.ReadToEnd(); 
    System.Text.Json.JsonDocument.Parse(json).Dump();    
}

But it is more easier to use GetStringAsync(url); which does this for you - for example

using (var client = new System.Net.Http.HttpClient())
{
    var url = "https://googlechromelabs.github.io/chrome-for-testing/last-known-good-versions-with-downloads.json";
    var json = await client.GetStringAsync(url);
    System.Text.Json.JsonDocument.Parse(json).Dump();
}

I'm not sure what you mean by a "Dump richtext format" ?

If you want to be able to expand or collapse sections of the json, then, AFAIK you can't do that in the rich text output panel, but can if you output to a grid/panel, e.g.

System.Text.Json.JsonDocument.Parse(json).Dump(true);

May I insist or should I create e new thread ?
KR

This is exactly what I was talking about, thanks for the fix

This will require writing a new C# outliner to avoid creating a dependency on the Roslyn stack, but that's actually not too difficult nowadays with AI. I've added this to the latest build; the new outliner also works with JavaScript.