This reminds me. How do you actually take astro-photos on a pixel? From what I've read, you just need to point it at the sky and the star button should appear. I have the 8 pro and have never seen it.
You need a tripod or something to rest the phone against. The prompt to take an astrophotography photo doesn't come up until the phone had been held VERY still for 5-10 sec.
You need to make sure your phone is very still before it appears. I usually will lay mine on a table or the top of a car and then tilt my head underneath it until it appears and when it does gently hit the button. I've gotten some pretty cool results from it like shooting stars and even the Milky Way.