wp_get_schedule and wp_next_scheduled don’t find my scheduled wp-cron job

Well, I found the answer in the actual documentation:
https://developer.wordpress.org/reference/functions/wp_next_scheduled/

in form of a comment by “ub3rst4r”:

Note the $args parameter! Not specifying the $args parameter in wp_next_scheduled but having $args for wp_schedule_event will cause many events to be scheduled (instead of just one).

Bad Example:

if ( ! wp_next_scheduled( 'myevent' ) ) { // This will always be false
    wp_schedule_event( time(), 'daily', 'myevent', array( false ) );
}

Good Example:

$args = array( false );
if ( ! wp_next_scheduled( 'myevent', $args ) ) {
    wp_schedule_event( time(), 'daily', 'myevent', $args );
}