Somehow the the_content function is called multiple times, resulting in duplicate links being displayed.

To resolve this issue you can use one of the options provided below.

Option 1: 

1. Navigate to the Dashboard > wpForo > settings > "Forum - Blog" Cross Posting  admin page and disable the "Display Cross-posted Topic Link on Blog Post" option.

2. Insert the following code into the active theme's functions.php file:

add_action( 'wp_head', 'twentynineteen_colors_css_wrap' );

add_shortcode('wpf_crossposting_link', 'wpf_display_crosspost_link');
function wpf_display_crosspost_link() {
    if(!function_exists('WPF') || !class_exists('wpForoCrossPosting')){
        return;
    }
    global $post;
    $content = '';
    $postID   = $post->ID;
    $boardids = get_post_meta($postID, '_wpforo_boardids', true);
    if (!$boardids) {
        $boardids = [];
        $boardids[] = 0;
    }

    foreach ( $boardids as $boardid ) {
        $board = WPF()->board->get_board( intval( $boardid ) );
        if ( ! $board ) {
            continue;
        }

        WPF()->change_board( $boardid );

        if ( ! wpforo_is_module_enabled( WPFOROCROSSPOST_FOLDER ) ) {
            continue;
        }

        $prefix = WPF()->generate_prefix( $boardid );

        if (is_singular() ) {

            $topicID                = get_post_meta( $postID,
                '_' . $prefix . 'crossposting_topicid',
                true );
            $isCrossPostingDisabled = get_post_meta( $postID,
                '_' . $prefix . 'crossposting_disabled',
                true );
            if ( $topicID && ! $isCrossPostingDisabled ) {
                $linkText = wpforo_phrase( 'This article is also published as a forum topic here', false );
                $topicURL = wpforo_topic( $topicID, 'url' );
                $content  = '<div class="wpfcp-article-info">';
                $content  .= '<a href="' . esc_url( (string) $topicURL ) . '">' . $linkText . ' &raquo;</a>';
                $content  .= '</div><div class="wpfcpcb"></div>';
            }

            return $content;
        }
    }
}

3. Use the shortcode within the post content:

Option 2:

The CSS code can be used as well:

.fusion-tb-footer.fusion-footer .wpfcp-article-info, #content .wpfcp-article-info {display:none;}
#content .post-content .fusion-content-tb .wpfcp-article-info{ display:block !important;}

https://www.sneaker-forum.nl/2024/02/air-jordan-1-high-og-wmns-dusted-clay-fq2941-200/

use this code instead of the above

.fusion-tb-header .wpfcp-article-info,
.fusion-post-cards .wpfcp-article-info,
.fusion-page-title-bar.fusion-tb-page-title-bar .wpfcp-article-info {display: none}

Thanks! 

use this code instead of the above

.fusion-tb-header .wpfcp-article-info,
.fusion-post-cards .wpfcp-article-info,
.fusion-page-title-bar.fusion-tb-page-title-bar .wpfcp-article-info {display: none}

add it to custom css

.fusion-tb-header .wpfcp-article-info, 
.fusion-page-title-bar.fusion-tb-page-title-bar .wpfcp-article-info {display: none}

Dashboard > wpForo > Settings > Colors & Styles > Custom CSS

Home - Sneaker Forum (sneaker-forum.nl)

Here you can see the 'This article is also published as a forum topic here »' underneath the post on the homepage.

https://www.sneaker-forum.nl/2023/12/nike-dunk-mid-panda-fq8784-100/

This is the post I cross-posted with the forum. The button with 'This article is also published as a forum topic here »' is everywhere on the page. 

The only place I want this button is in the right corner underneath the post.

You can see two 'More discussion »' links above the post, the correct one underneath the gallery and way down to the bottom of the page another one.