您需要在DownloadHandler.cs中实现IDownloadHandler接口

public class DownloadHandler : IDownloadHandler
{
    public event EventHandler<DownloadItem> OnBeforeDownloadFired;
    public event EventHandler<DownloadItem> OnDownloadUpdatedFired;

    public void OnBeforeDownload(IBrowser browser, DownloadItem downloadItem, IBeforeDownloadCallback callback)
    {
        OnBeforeDownloadFired?.Invoke(this, downloadItem);

        if (!callback.IsDisposed)
        {
            using (callback)
            {
                callback.Continue(downloadItem.SuggestedFileName, showDialog: true);
            }
        }
    }

    public void OnDownloadUpdated(IBrowser browser, DownloadItem downloadItem, IDownloadItemCallback callback)
    {
        OnDownloadUpdatedFired?.Invoke(this, downloadItem);
    }
}

用法：

var browser = new ChromiumWebBrowser();
browser.DownloadHandler = new DownloadHandler()

((DownloadHandler)browser.DownloadHandler).OnBeforeDownloadFired += (sender, args) =>
{
    // Display the file save dialog
};

((DownloadHandler)browser.DownloadHandler).OnDownloadUpdatedFired += (sender, args) =>
{
    // Update the download progress
};