WP Get ACF Repeaters by Value ... working

function exercise_shortcode( $atts ) {
    //shortcode atts
    $atts = shortcode_atts( array(
        'muskelgruppe' => 'rücken',
    ), $atts, 'exercise' );

    //Get Muskelgruppe from shortcode atts
    $muskelgruppe = $atts['muskelgruppe'];

    //Get only Posts with a Repeater
    $exercises = get_posts(
        array(
            'post_type'      => 'post',
            'posts_per_page' => 500,
            'meta_query'     => array(
                'relation' => 'AND',
                array(
                    'key'     => 'uebungen',
                    'compare' => 'EXISTS',
                ),
            ),
        )
    );

    $output = "";
    //Loop
    if ( $exercises ) {
        foreach ( $exercises as $exercise ) {
            setup_postdata( $exercise );
            if( have_rows('uebungen',$exercise->ID )) {
                while( have_rows('uebungen',$exercise->ID) ) : the_row();
                    if( $muskelgruppe == get_sub_field('uebung_gruppe')) {
                        //Hier kannst du deine gewünschten Felder abrufen
                        $exercise_title = get_sub_field('uebung_name');

                        //Dem Output anfügen
                        $output .= '<div class="uebung">';
                        $output .= '<p>';
                        $output .= $exercise_title;
                        $output .= '</p>';
                        $output .= '</div>';
                    }

                endwhile;
            }
        }
        wp_reset_postdata();
    }
    return $output;
}

add_shortcode( 'exercices', 'exercise_shortcode' );

// Use [exercices muskelgruppe="xyz"]