Can you SSH into your ‘cron’ instance and run ps aux | grep cron and see if you get a result for ‘cron -f’ ?
when you run cron -f command it essentially looks for a directory like etc/cron.d/ and loads cron jobs defined in this location.
Uploading your Dockerfile would help in understanding if there’s any issue.
You might find solutions in this post to be useful-Laravel Scheduler Cron Not Working