I know what you mean and what you wish to have on this Valentine’s day!
If you wish to kinds of “attach” file to email which is generated by the action, probably you can do this sort of workaround.
Before you start to send the email by action, you need to store the “file” you want to attach to that email action. What is the attachment file you want to send along with email? Is it file you save on that table? or any file like PDF you only can get and being generated through Appsheet workflow? If it is file you save on the app, it means you do have files saved in your cloud service when you run the action. Meaning you can generate the access URL upon saving those files to your cloud. Then when you generate the action, you place the column in the email body. When your email receiver get email by action, they can find the url link in the email body. This is not physically attaching file to the email, but the email receiver will have access to the file through the URL.
In case the file are only generated by workflow, then you make action which does sequence of action. First action will fire the workflow to generate the PDF (or any other file type) and save file in your cloud. The second action will send email with email body which include the URL to the file you generated through the first action which fire workflow on the backend.
At the time your user receive or view your email, the appsheet is probably finishing the task at the backend to generate and save the file through the workflow, meaning ,the URL is not dead but live at the time they click the link (URL) on the email body.
Hope make sense.