I ran the following WP-CLI command on a WordPress site recently to see all the active crons and was surprised at how many crons there were from plugins that don't exist on the website.

bash

wp cron event list

My guess is that these are leftover crons from plugins that used to be installed on the website. Obviously if the plugin is gone, its crons should no longer be on the website so I ran the following for each cron to remove it from the site.

bash

wp cron event delete cron_name