I don’t know any theme component that shows a pop up after sign up, but it should be possible, and you could check some of the user’s stats to show it only to new users (maybe a reading time of 0; I don’t think “seen” works).
I was wondering if a personal message sent to the user might also work. There are some options on how to send users a message once they join. I’d need to check which one works best for this case.
With User Field Prompt component, the information could even be entered directly in the message.
