This page is titled "Use Map Components (React 19 + Web Components)" and it provides instructions to download the SDK to a new folder on your ExB development environment called "web-component-widgets/use-web-components-19". React JS 19 uses functional components. Under the "Contents" version it states:

The issue I see is that at the SDK location it still uses class components. For example, the "add-layers" sample it states that it was updated to version 1.19 but the script suggests otherwise.

render () {
const style = css`
form > div {
display: flex;
justify-content: space-between;
input {
width: 100%;
}
button {
min-width: 100px;
}
}
`
return (
<div className="widget-addLayers jimu-widget p-2" css={style}>
{this.props.hasOwnProperty('useMapWidgetIds') &&
this.props.useMapWidgetIds &&
this.props.useMapWidgetIds.length === 1 && (
<JimuMapViewComponent
useMapWidgetId={this.props.useMapWidgetIds?.[0]}
onActiveViewChange={(jmv: JimuMapView) => {
this.setState({
jimuMapView: jmv
})
}}
/>
)}
<p>{defaultMessages.instructions}</p>