Trying to add categories to shortcode of simple plugin – help!

Hi! I am working on a project where the goal is to display upcoming events but to have the different categories of events shown on individual pages – so to do this I will need to add to the existing shortcode so I can tell it what category ID to display. I am using the plugin Upcoming Events Lists and have already added the option to select categories in each event post in the back end. I can understand how things fit together from reading basic documentation but I am having trouble implementing it.

What I need help with is adding to the plugin's shortcode and the code after to tell it to only display events from a particular category. I am thinking that I just need to edit the Frontend.php file but if it seems like I am missing anything, I can provide more code! It is a fairly simple plugin so there are not many files to it. What do I need to add to this code?

<?php

namespace UpcomingEventsLists\Frontend;

use UpcomingEventsLists\Event;

// If this file is called directly, abort.
defined( 'ABSPATH' ) || exit;

class Frontend 

/**
 * The instance of the class
 *
 * @var self
 */
private static $instance;

/**
 * Ensures only one instance of the class is loaded or can be loaded.
 *
 * @return self
 */
public static function init() 
if ( is_null( self::$instance ) ) 
self::$instance = new self();

add_action( 'wp_enqueue_scripts', array( self::$instance, 'frontend_scripts' ) );
add_filter( 'the_content', array( self::$instance, 'single_event_content' ) );
add_filter( 'the_content', array( self::$instance, 'archive_event_content' ) );
add_shortcode( 'upcoming_events_list', array( self::$instance, 'upcoming_events_list' ) );


return self::$instance;


/**
 * Render upcoming events list html
 *
 * @return string
 */
public function upcoming_events_list( $attributes ): string 
$attributes = shortcode_atts( array(
'show_all_event_link'   => 'yes',
'view_type'             => 'list', // 'list' or 'grid'
'columns_on_tablet'     => 2,
'columns_on_desktop'    => 3,
'columns_on_widescreen' => 4,

), $attributes, 'upcoming_events_list' );



$view   = 'grid' === $attributes['view_type'] ? 'grid' : 'list';
$events = Event::get_events();
ob_start();

$classes                = [ 'upcoming-events-list', $view . '-view' ];
$classes_item_container = [ 'upcoming-events-list-container' ];
if ( 'grid' === $view ) 
$classes[]                = 'shapla-columns is-multiline';
$classes_item_container[] = static::column_to_class( $attributes );

?>
        <div class="<?php echo esc_attr( join( ' ', $classes ) ) ?>">
<?php
foreach ( $events as $event ) 
echo '<div class="' . esc_attr( join( ' ', $classes_item_container ) ) . '">';
$event->get_event_card();
echo '</div>';

?>
        </div>
<?php if ( 'yes' === $attributes['show_all_event_link'] )  ?>
            <a class="upcoming-events-list-button" href="<?php echo get_post_type_archive_link( Event::POST_TYPE ); ?>">
<?php esc_html_e( 'View All Events', 'upcoming-events' ); ?>
            </a>
<?php


return ob_get_clean();


private static function column_to_class( array $attributes ) 
$defaults = [
'columns_on_phone'      => 1,
'columns_on_tablet'     => 2,
'columns_on_desktop'    => 3,
'columns_on_widescreen' => 4,
];
$maps     = [ 1 => 12, 2 => 6, 3 => 4, 4 => 3, 6 => 2 ];
$attrs    = [];
foreach ( $defaults as $key => $default ) 
$number        = isset( $attributes[ $key ] ) ? intval( $attributes[ $key ] ) : $default;
$number        = min( 6, max( 1, $number ) );
$attrs[ $key ] = $maps[ $number ] ?? - 1;


$classes = [ 'shapla-column', sprintf( 'is-%s-tablet', $attrs['columns_on_tablet'] ) ];
if ( $attrs['columns_on_desktop'] < $attrs['columns_on_tablet'] ) 
$classes[] = sprintf( 'is-%s-desktop', $attrs['columns_on_desktop'] );

if ( $attrs['columns_on_widescreen'] < $attrs['columns_on_desktop'] ) 
$classes[] = sprintf( 'is-%s-widescreen', $attrs['columns_on_widescreen'] );


return join( ' ', $classes );


/**
 * Enqueueing styles for the front-end widget
 */
public function frontend_scripts() 
if ( ! $this->should_load_frontend_script() ) 
return;

wp_enqueue_style( UPCOMING_EVENTS_LISTS . '-frontend' );


/**
 * Check if frontend script should load
 *
 * @return bool
 */
public function should_load_frontend_script(): bool 

/**
 * Check if archive-event.php file loaded in theme directory
 *
 * @return bool
 */
private function has_event_archive_template() 
if ( locate_template( "archive-event.php" ) != '' ) 
return true;


return false;


/**
 * Check if single-event.php file loaded in theme directory
 *
 * @return bool
 */
private function has_event_single_template() 
if ( locate_template( "single-event.php" ) != '' ) 
return true;


return false;


public function archive_event_content( $content ) 
if ( is_post_type_archive( Event::POST_TYPE ) ) 
if ( $this->has_event_archive_template() ) 
return $content;



return $content;


/**
 * @param  string  $content
 *
 * @return string
 */
public function single_event_content( $content )