Hey there! It is possible to create custom remote backup destinations using the "Custom" option as outlined here:
docs.cpanel.net
We have an older example of setting up Dropbox, but since it's from 2018 I'm not sure if the screenshots and details are still 100% accurate. However, it does show that this is possible to configure:
Backup Configuration | cPanel & WHM Documentation
The Backup Configuration interface allows system administrators to customize their scheduled backups.
docs.cpanel.net
We have an older example of setting up Dropbox, but since it's from 2018 I'm not sure if the screenshots and details are still 100% accurate. However, it does show that this is possible to configure:
Custom Backup Transport: Dropbox | cPanel Blog
One of the best features the ability to add custom remote destinations. This post takes you through using Dropbox as your storage for your cPanel & WHM Backups.
blog.cpanel.com
Thank you. Wonder why Dropbox not included in Additional Destinations under Custom backup in WHM.
We try to include a good number of options by default, but can't include everything. You could always submit a feature request using the link in my signature if you'd like to see that added to the product, and I'll make sure that gets brought up with our developers.
