Weird. I found out that shift+return does a carriage return, but option+return submits (option+return is how Slack does it).

I didn't steal the extended keyboard from my daughter to see how enter (as opposed to return) works but note that this feedback site defaults to return being a c/r and requiring submit button to submit.

Agreed!! It would be much better if hitting "Enter" added a hard return in the Action Card content rather than posting the comment.

Totally agree! We get double notifications or even triple sometimes due to our users accidentally hitting return.