Hi there,
Please check out this sample as it shows what you are trying to achieve: https://developers.arcgis.com/javascript/latest/sample-code/sandbox/?sample=client-projection
The following is the code and it waits until layer's layerView.updating becomes false when the app loads first. The LayerView.updating becomes false once it finishes updating.
view.whenLayerView(countriesLayer).then((layerView) => {
watchUtils.whenFalseOnce(layerView, "updating", () => {
// enable the projection dropdown
wkidSelect.disabled = false;
calciteLoader.removeAttribute("active");
});
});