PuppeteerSharp downloads a csv with headless=false. How to do it with headless=true?

Question

The C# statement that clicks the download button is:

await frameContent2.ClickAsync("a[class='exportIconOld']");

The HTML tag is:

<a class="exportIconOld" href="javascript:onLink();" onclick="PGL.JOL.getTypeFromElement(this, new PGL.JOL.Types('ui:table')).exportTable();" title="Export To Excel"></a>

Or I could ask "In what way does headless=true change the behaviour?" Advice on either question would be very helpful.