You asked

Is the sony fe 14mm f 1 8 gm good in low light?

Here is what the site says about that.

From Sony FE 14mm f/1.8 GM: Sony FE 14mm f/1.8 GM: A prime lens by Sony for Full frame cameras, 14mm f/1.8. Specs - Maker: Sony - Focal length: 14mm (prime) - Maximum aperture: f/1.8 - Made for: Full frame sensors - Mounts: Sony E - Stabilised: no - Autofocus: yes What it frames like - On full frame (Sony E): as marked, 14mm. - On APS-C (Sony E): like 21mm on full frame; f/1.8 gives about the depth of field ...

From Sensor sizes: Is full frame worth it?: For low light, events, and portraits with very shallow depth of field, yes. For travel, street, wildlife on a budget, and most hobby photography, a good APS-C camera with good lenses is enough, and you'll carry it more. Lenses and light matter more than the last stop of sensor performance.

Quoted from this site's pages.

From these pages