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

https://github.com/nakamura196/omekac_backup

I also created a Google Colab notebook that demonstrates how to run this program.

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

In the above tutorial, data download is performed targeting the following Omeka Classic site.

https://jinmoncom2017.omeka.net/

After execution, the API download results are output to the docs folder.

You can use the above data for backups, etc. I hope this serves as a useful reference when using Omeka Classic.