Hi David!
A few things have changed since then and there is indeed an easier, safer way:
function __return_1000() {
return 1000;
}
add_filter( 'tribe_events_community_category_dropdown_shown_item_count', '__return_1000' );
Some code like the above, which you could add either to a custom plugin or – if you need to/prefer to – your theme or child theme’s functions.php file, ought to do the trick. In the unlikely event you have more than 1,000 categories you could of course increment the value here:
return 1000;
Hope that helps 🙂