Adds a named SPFx web part to a SharePoint page - simple example with hard-coded values.

addSPFxWebPart.cs

private static void addModernWebPartToPage(ClientContext siteContext)
{
    Console.WriteLine(string.Format("addModernWebPartToPage(): Entered."));

    // get page context - the actual name/page instance is specified in the Save() method..
    ClientSidePage page = new ClientSidePage(siteContext);

    // get the available web parts - this collection will include OOTB and custom SPFx web parts..
    var components = page.AvailableClientSideComponents();

    // name is actually the ID of the web part, based on the table elsewhere in this article..
    string wpName = "daf0b71c-6de8-4ef7-b511-faae7c388708";

    // add the named web part..
    var webPartToAdd = components.Where(wp => wp.ComponentType == 1 && wp.Name == wpName).FirstOrDefault();
    if (webPartToAdd != null)
    {
        ClientSideWebPart clientWp = new ClientSideWebPart(webPartToAdd) { Order = 10 };
        page.AddControl(clientWp);
    }

    // the save method creates if not exists..
    page.Save("COBModernPage1.aspx");

    Console.WriteLine(string.Format("addModernWebPartToPage(): Leaving."));
}