It's not the most obvious, but it might still be there. If you have any other things in the Service NSW app like a driver or boat driver licence, the COVID certificate is not immediately obvious and you have to swipe the other items away first until you can see the COVID certificate. Here is what mine looks like:In that case, it isn't working. The Medicare app says that it's linked. I'll scratch my head for a while....
First thing I see when I open the app is boat licence.
So swipe this away to the left, and then you see:
Edited: I see you have fixed it @jb747 - But I will leave this here in case it helps any one else find the certificate.