Where do the files downloaded from Gmail (which were received as attachments) go in the Files app? I am not able to locate them.
Initially, they're in a temp folder. If you tap and hold, you'll be able to save somewhere directly.
If you want to save the a photo, open the individual attachment by tapping on it after the download is complete, then tap Save and it will get saved to your Saved Photos folder
If it is a document, it's a little funnier. You have to open the "Office" app and then select "email: opened attachments"
I haven't been able to find where PDFs go yet.