And there is a way to overcome this without using Box or Drive, etc; it’s just ugly as heck.
In Autocode, build a web service that sustains your text blob for 60 seconds (they have examples of this). Then (in Airtable script or any scripting environment for that matter) call that service passing your text. It will return a signed URL that’s valid for 60 seconds. Then hand that URL off to Airtable as you save the attachment field. It works very well and it’s really fast but it does require a trip around the barn.
I’m surprised mini-extensions (and even Airtable) have not created such a temporary URL proxy service but I guess there could be a boatload of content security issues depending on your use case. BTW - this also works for images, videos and just about any file type. The free tier of Autocode is typically all you need.