I just figured that you can send "Enter" via ^M, for testing all commands:

Start a new session called hurra: screen -AmdS hurra

Send a command (or do it multiple times for testing): screen -S hurra -p 0 -X stuff "date^M"

Quit session: screen -S hurra -X quit

(just figured this out to continue work on automatic ssl/LetsEncrypt updater)