I created a program to download Omeka S data. It is published in the following repository.

https://github.com/nakamura196/omekas_backup

I also created a Google Colab showing an execution example of this program.

https://colab.research.google.com/github/nakamura196/ndl_ocr/blob/main/omekas_backup.ipynb

In the above tutorial, data download is executed targeting the following Omeka S sandbox.

https://omeka.org/s/download/#sandbox

After execution, API download results are output to the docs folder, and an MS Excel file summarizing them is output to the data folder.

The above data can be used for backups and other purposes. I hope this is helpful when using Omeka S.