Ok, so all cronjobs have been deleted.
So back to automatically starting on System Boot. You had indicated to follow guidelines in the documentation link: https://docs.bitnami.com/installer/faq/linux-faq/administration/autostart-linux/
When checking the existing etc/init.d I can see the earlier 'bitnami' script that started applications in the opt/bitnami/ environment. So I would guess that I would need to delete this original script and replace with the copy of the script from /opt/magento-2.3.3-1 ctlscript.sh as detailed in the Link you had previously provided?
For a cleaner overall result, could you see any disadvantage in my Spinning up a new Ubuntu 18.04LTS OS Only Lightsail instance and then installing the latest Linux bitnami-magento-2.3.3-3-linux-x64-installer.run using the same instructions you had provided (with the exception of the removal of the older/previous magento stack since it wouldn't be there in the first place)? I Guess this was one of davidg's suggestions on 11/01/19 but I hadn't entirely understood the benefits of doing it that way until possibly now.