You’re running into two main issues: light pollution and very high ISO noise.

The yellow glow/bright lower part of the frame is most likely stray light pollution from nearby streetlights or the horizon. It doesn’t take much artificial light to wash out dim stars.

The heavy grain and colored streaks are noise from using ISO 12800, especially in a dark scene. High ISO boosts both the signal and the sensor’s noise. Your G1 X is capable, but like most compact-style cameras it will struggle more than larger-sensor cameras in very low light.

Try this instead:

• Use a tripod
• Keep the lens at f/2.8
• Lower ISO to about 1600–3200
• Increase shutter time to roughly 15–20 seconds, while using the “500 rule” as a guide to avoid star trailing
• If longer exposures blow out, your sky is likely being brightened by light pollution
• Consider stacking multiple exposures to reduce noise

The biggest improvement will usually come from shooting from a darker location with less skyglow. In short: lower ISO, longer exposure, stable support, and darker skies.