There are tonnes of solution available I believe which will be able to help you to convert your xlsx to csv in an automated manner. If attachments are coming in email from a erp or bank or some other software, they almost always will have solution for csv as well.
Here are few I found from Google Search
https://stackoverflow.com/questions/5256733/convert-xlsx-file-to-csv-using-batchhttps://github.com/dilshod/xlsx2csv---
Time for a story
Few years back I had used a super convoluted solution where emails were downloaded automated by using TheBat! email client (on Windows) which allows to save all attachment in a folder, then on MacOSX using Hazel(app), will use a command line tool would scan the files to csv , Hazel (app) would then move it to GDrive.
It worked for few months (but would require constant tweaks every week).
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Prashant Maheshwari
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