It is not displayed on the map. I went to create a layout and it automatically displays at the bottom of the layout with no service layer credits as dynamic text applied by me.
Interesting, I've never seen that happen before. Can you tell me what version of Pro you are using and what basemap? There might be a bug somewhere. In the meantime, you can add dynamic text for the service layer credits and style it to fix your layout. This 1 min tutorial shows you how: https://www.youtube.com/watch?v=Zm96Qiy8gy0