file uploading field – we do not get any attachments

Did you add the mail-tag at “File attachments” in mail tab?

See also https://contactform7.com/file-uploading-and-attachment/

See File Uploading and Attachment. There is limit option of [file] tag. You can use it like this:

[file your-file filetypes:pdf|txt limit:2mb] Also note that PHP configuration settings affect the allowed file size.
You should also check for upload and email limits imposed by your WordPress hosting.