In regards to backup of my Mac Mini M1 and DEVONthink, my concept is as follows:
I use TimeMachine to automatically backup my system over USB to a SSD, beside some excluded folders, like for local DT backup archives, Downloads and some others.
Just in case, as it does not hurt and is both encrypted and automatic.
My main data is but on an external APFS-encrypted Thunderbolt drive, or in DEVONthink.
I have OneDrive set up with the Sync / Cache location on that external drive, all content pinned.
As I do not trust any Cloud provider, lots of content is encrypted with Cryptomator, which can be mounted on the Mac as regular volume.
DEVONthink is configured to sync to a remote WebDAV server and additionally to OneDrive (the local Sync Location, which get’s uploaded to OneDrive).
This saves my databases encrypted to those remote locations.
On my WebDAV server I create and rotate backups from time to time, but rarely.
I have some imported DT databases, some open, some as encrypted disk images.
Also, I started to index one of my Cryptomator Volumes, which will be the way to go, for me.
I plan to migrate all content to Cryptomator, which is stored on OneDrive and over DT synced to both WebDAV and OneDrive (the indexed database itself is not sync again to OneDrive, but all others).
Then, every few days, after adding or changing something, I back-up the OneDrive data to local VeraCrypt encrypted disks, one SSD and two HDD which I weekly rotate as archives.
This backup is simply done with “rsync” and a bash script.
The same is done to my Cryptomator content, which removed this content from the need of working Cryptomator software - the backup contains the unencrypted files, but on an encrypted volume.
And finally, my /Users/tja folder will be copies to those VeraCrypt volumes too - and here, I am not sure about what should be saved and what not.
Lots of stuff below ~/Library seems obsolete.
This is, because I don’t trust Microsoft - I already lost one account and hundreds of GB of content due to Microsoft closing this account.
This could happen at any time.
So, I use OneDrive but always expect it to vanish. A family account with about 69 Euro yearly for 6TB is hard to beat.
The same goes for my Cryptomator volumes - at any time after a macOS update, this may cease to work.
Making regular backups / archives to local VeraCrypt disks ensures that I could “survive” both a OneDrive shutdown and a Cryptomator update problem.