“When you use Signal, your data is stored in encrypted form on your devices. The only information that is stored on the Signal servers for each account is the phone number you registered with, the date and time you joined the service, and the date you last logged on.”
I’m not sure actually. I just tried to screen record and it wouldn’t let me. Then I tried to take a screenshot and it triggered a no screenshots pop-up
You can do with another device (i.e. filming the screen). It is of course less convenient, but that’s it.