exclude spesific kategori on all post query

add_action(
    'pre_get_posts',
    function ( $q ) {
        if ( is_admin() ) {
            return;
        }
        $post_type = $q->get( 'post_type' );
        if ( empty( $post_type ) ) {
            $post_type = 'post';
        }
        if ( is_array( $post_type ) || 'post' !== $post_type ) {
            return;
        }

        $excluded_cat_id = 1; /* Change this with your exclulded category ID  */

        $cat_in = $q->get( 'category__in' );
        if ( ! empty( $cat_in ) ) {
            if ( ! is_array( $cat_in ) ) {
                $cat_in = array( $cat_in );
            }
            $cat_in = array_map( 'intval', $cat_in );

            if ( in_array( intval( $excluded_cat_id ), $cat_in, true ) ) {
                return;
            }
        }

        $existing = $q->get( 'category__not_in' );

        if ( empty( $existing ) ) {
            $existing = array();
        } elseif ( ! is_array( $existing ) ) {
            $existing = array( $existing );
        }
        $existing = array_map( 'intval', $existing );

        $existing[] = $excluded_cat_id;
        $merged     = array_values( array_unique( $existing ) );

        $q->set( 'category__not_in', $merged );
    }
);