Shows PnP core methods to create/modify modern SharePoint pages.

createOrModifyModernPage.cs

private static void createPage(ClientContext siteContext, string pageName)
{
    ClientSidePage page = new ClientSidePage(siteContext);

    ClientSideText txt1 = new ClientSideText() { Text = "COB test" };
    page.AddControl(txt1, 0);

    // page will be created if it doesn't exist, otherwise overwritten if it does..
    page.Save(pageName);
}

private static void modifyExistingPage(ClientContext siteContext, string pageName)
{
    // load exising page - will return null if no page found with this name..
    ClientSidePage page = ClientSidePage.Load(siteContext, pageName);

    ClientSideText txt1 = new ClientSideText() { Text = "COB test" };
    page.AddControl(txt1, 0);

    page.Save(pageName);
}