How do I add a template to a theme using a plugin?

I need a page template to be used with my plugin. I don’t need to replace a theme template such as single or archive.

Normally I’d use

/*
* Template Name: Blah Blah Blah
*/

to add a template to the page options, however, this isn’t working in the plugin, as expected. I know how to add a template for a custom post type in a plugin. However, I need this to be an option the templates dropdown in the page options.

Here is a fairly simple approach I was able to get working within a plugin. You’ll want to reference https://developer.wordpress.org/reference/hooks/theme_page_templates/ and https://developer.wordpress.org/reference/hooks/template_include/ as you review the code below.

<?php
//Add our custom template to the admin's templates dropdown
add_filter( 'theme_page_templates', 'pluginname_template_as_option', 10, 3 );
function pluginname_template_as_option( $page_templates, $theme, $post ){

    $page_templates['template-landing.php'] = 'Example Landing Page';

    return $page_templates;

}

//When our custom template has been chosen then display it for the page
add_filter( 'template_include', 'pluginname_load_template', 99 );
function pluginname_load_template( $template ) {

    global $post;
    $custom_template_slug   = 'template-landing.php';
    $page_template_slug     = get_page_template_slug( $post->ID );

    if( $page_template_slug == $custom_template_slug ){
        return plugin_dir_path( __FILE__ ) . $custom_template_slug;
    }

    return $template;

}