Sorry, just seeing this thread now for the first time!
I was able to get the attachments to appear in the Attachments field by choosing this path:
The “Find Records” step > “Records” > “Field Values” > the Attachment field > then where it says “Flatten”, choose “Insert”.
The CSV format is not supported by Automations at this time.
To workaround this problem, you would likely be able to write a custom script to handle this for you. Or if you’re looking for a low-code way of handling this, you could use my favorite automation tool Integromat, which has built-in CSV integrations: