Hi,
If you open the cron URL with your browser and the Cassiopeia template activated and the cron and plugin configured to trigger every second (so that you're sure the plugin is triggered when you open the cron URL) and with the debug of the joomla configuration activated on your website, you get this error page:
i.imgur.com/0UOdCOe.png
This error indicates that in a product description, you have a loadmodule / loadposition tag for a module which has been deleted or is not accessible.
Also, there is a problem in the loadmodule plugin of Joomla. It should have some kind of soft fail so that if it can't find a module for one reason or another, it just gracefully remove the tag and log the problem instead of crashing.
Because of both of these, it leads to the google products plugin being stopped in the middle and thus it can't finish generating the XML.
What's strange is that the problem doesn't happen when manually generating the XML in the backend with the trigger button. Usually, with similar issues, it does and thus it is easier to find out what the problem is.
I've made some changes in the google products plugin so that if something fails during the product description processing by content plugins, the error is ignored. I've added the changes on your website and now I can run the cron URL without the fatal error.
That also means that somewhere on your frontend, you must have a product with doesn't display properly because its description can't be processed due to that same content tag.
I now see some messages from the plugin :
Google Merchant file written to /home/safety/public_html/productfeed/szsproducts.xml
Cannot connect to partnerupload.google.com:19321. Error 101. Network is unreachable
OpenAI feed written to /home/safety/public_html/productfeed/openai_feed.json
So it seems it can write the files properly now, but the credentials for the FTP access of Google Merchants don't seem to work or your hosting is blocking the connection to Google Merchants as part of his security mechanisms.