alternative.php

//uses single template but not as good for theme compatability
<?php
function custom_template_snippet_post_type_plugin( $single ) {
      global $wp_query, $post;
      if ($post->post_type == "sdr_snippet"){
        // if in subfolder
        $template = plugin_dir_path( __FILE__ ) . 'templates/single-snippet.php';
          
        // if in plugin root directory folder
        //$template = plugin_dir_path( __FILE__ ) . '/single-snippet.php';
        // directory folder file
        //$template = dirname( __FILE__ ) . '/single-snippet.php';
        
          if(file_exists( $template ))
          return $template;
      }
      return $single;
    }
add_filter('single_template', 'custom_template_snippet_post_type_plugin');
?>

// THEN SINGLE WOULD LOOK SOMETHING LIKE THIS
<?php
function print_snippet_single_post() {
    $language = sdr_snippet_get_language( get_the_ID() );
	$html = '';
	$html .= '<div class="sdr-snippet-container" data-language="' . esc_attr( $language ) . '" data-show-lines="true" data-height="0">';
	$html .= '<pre class="sdr-snippet-box">';
	$html .= esc_html( get_the_content() );
    $html .= sdr_enqueue_frontend();
	$html .= '</pre>';
	$html .= '</div>';
	return $html;
}
get_header();
echo print_snippet_single_post();
get_footer();
?>

not_an_answerr.php

<?php
    if ( $post = get_post( $page_id ) ) {
        setup_postdata( $post ); //  "posts" page is now current post for most template tags        
        the_content();
        wp_reset_postdata(); // So everything below functions as normal
    }

snippets_done_right.php

// THIS WAY WORKS FOR SURE
<?php
function print_snippet_single_post($content) {
	$postid = get_the_ID();
        $post_type = get_post_type( $postid );
    if ( is_singe( $postid ) ){
        if (have_posts()) : 
        	the_post();
        // echo sdr_do_shortcode_snippet( $atts );
        $language = sdr_snippet_get_language( $postid );
	$html = '';
	$html .= '<div class="sdr-snippet-container" data-language="' . esc_attr( $language ) . '" data-show-lines="true" data-height="0">';
	$html .= '<pre class="sdr-snippet-box">';
	$html .= esc_html( get_the_content() );
	$html .= '</pre>';
	$html .= '</div>';

        if ( $post_type == "sdr_snippet") {
             return $html;
        }
        else {
	     return $content;
        }
        endif;
    }
    //  wp_reset_postdata();
}
add_filter( 'the_content', 'print_snippet_single_post', 10 );

working.php

function print_snippet_single_post($content) {
        $post_type = get_post_type( get_the_ID() );
        $language = sdr_snippet_get_language( get_the_ID() );
	$html = '';
	$html .= '<div class="sdr-snippet-container" data-language="' . esc_attr( $language ) . '" data-show-lines="true" data-height="0">';
	$html .= '<pre class="sdr-snippet-box">';
	$html .= esc_html( get_the_content() );
	$html .= '</pre>';
	$html .= '</div>';

        if ( $post_type == "sdr_snippet") {
             return $html;
        }
        else {
	     return $content;
        }

}
add_filter( 'the_content', 'print_snippet_single_post', 10 );