After version 4.28, the visual variable: opacity setting does not affect the outlines of SimpleMarkerSymbols.
This can be recreated in this sample:
https://developers.arcgis.com/javascript/latest/sample-code/sandbox/?sample=visualization-vv-color-a...
by changing the version in the header to 4.28
<script src="https://js.arcgis.com/4.28/"></script>
and changing the symbol to a simple marker with an outline.
symbol: {
type: "simple-marker",
color: "rgb(0, 0, 0)",
outline: {color: "red", width: 2}
},
If the version is above 4.28, the outline does not disappear as you move the slider.
