Backup tables app data

Hi
i recently started using the tables app.
As far as i can see, it does not save the sheets in a file on the nexcloud.
Thus i would like to know how do i make a backup of the tables there?
Each table has the posibility to import and export it.
The export gives a JSON file which the import does not accept.

I have installed nextcloud on a TrueNAS installation.
I have not tackled how to back the whole NC… but am confident, because i have the files on multiple computers/disks.
However i do not know where the varius apps save their data.
and before i start to use tables-app heavily i would like to know how to make a backup that can be easily restored on a fresh install of nexcloud?

So that should be your next task with top priority.

Thank you.
any sugestion which one to use for an installation thats made on truenas?