I got the same problem. Simply trying to show the legend with the "legend" keyword in the panel no longer works.
Code I use to create the panel item:
item.panel = new LayerListItemPanel({
content: "legend",
className: "esri-icon-legend",
title: "Show legend",
flowEnabled: true,
visible: true
});
The result is that no legend is showing and the action icon also doesn't show properly:
Calcite setup in my index.html:
<script src="https://js.arcgis.com/calcite-components/2.6.0/calcite.esm.js" type="module"></script>
<link rel="stylesheet" href="https://js.arcgis.com/calcite-components/2.6.0/calcite.css" />
<link rel="stylesheet" href="https://js.arcgis.com/4.29/esri/themes/light/main.css" />