How to backup Time Machine's backup to a cloud?
You should use multiple levels of backups, not a series of backups.

The difference being with a "series" of backups (backup of a backup of a backup etc.) you run the risk of backing up garbage if there is a failure making subsequent backups worthless (think of a failed bulb in a string of Christmas tree lights).

It's also important to note that backup is a strategy, not a product you buy.

Having multiple levels of backups works by taking different paths to securing your data.  The key here to recovery is to not get your system back up and running, but being able to get back working as quickly as possible.  

To illustrate the difference and the usefulness of this strategy, think about what you would do if something catastrophic happened (your Mac physically blew up) and you couldn't get another Mac for a week, but had access to a PC. 


Time Machine backup for the whole system
Documents &amp; Data 


Replicated to on site NAS
Synced with OneDrive cloud service

Application settings (Preferences, templates, etc.)


Synced to iCloud drive
Replicated to on site NAS
Synced with OneDrive cloud service



As for the NAS, (I personally) use one with a with RAID one for hard drive redundancy with multiple USB hard drives for backing that up.   How is this configured?


NAS with RAID HDDs


USB backup for whole system
USB backup for incremental daily backups
Synchronization with additional cloud service (OneDrive, DropBox)



What does all of this accomplish?

Let's take a look at a single document (maybe a payroll spreadsheet):

Document -&gt; Time Machine
         -&gt; Sync to OneDrive
         -&gt; NAS -&gt; RAID Array
                -&gt; NAS backup to USB drive
                -&gt; Selected volume backup to USB drive
                -&gt; Selected volume sync to OneDrive


What this means is that your document is in many places with three different paths minimizing the chance of data loss if any one path fails. Also, by not depending on Time Machine as the only backup strategy, you can get back working if you are in a situation where you have no access to an equivalent or newer Mac.

Does this work?

Absolutely.  I run at least 3 VMs on my iMac and when the HDD crashed I had everything back up and running on a PC I had the garage running within 30 mins while I waited for the replacement parts to arrive.

Could I have used dedicated for pay services?  Certainly, but if you depend only on what's out of the box with these services and not strategically implement their services, you may end up with backups of data that are of no use.