attachment sent using Geary ends up with CRLF terminators
I'm running Geary from mainline (OK, actually from mjog/986-namespace-assert, though I doubt that matters) on Ubuntu 20.04.
If I use Geary to send a plain text file with Unix line terminators (LF) from myself to myself, and I then read my email using a web browser and save the plain text attachment to a text file, it ends up with CRLF terminators.
This happens both when (a) I send from my Gmail account to my own Gmail account and read it using the Gmail web client, and also (b) when I send from my university mail account to the same account, and read the mail using our Roundcube web client. (I think this university mail might be hosted using Dovecot, though I'm not sure.)
Because I see the same phenomenon with two different mail servers/web clients, I think this is probably Geary's fault.