For astrophotography, wider is often better, and 20mm is a key focal length.
This page looks at the f/2 performance of the Nikon NIKKOR Z 20mm f/1.8 S on an 11-minute exposure.
Nikon NIKKOR Z 20mm f/1.8 S: Astrophotography at f/2
Includes len analysis along with commentary of the Nikon Z7 image quality (poor).
Stars above White Mountains
f2 @ 659.0 sec LENR enabled, ISO 64; 2020-08-13 21:42:55[low-res image for bot]
NIKON Z7 + Nikon NIKKOR Z 20mm f/1.8 S
ENV: White Mountains, altitude 10500 ft / 3200 m, 60°F / 15°C
RAW: LACA corrected, distortion corrected