About Charging of my iPhone xs

There are two possibilities:

1. You are using a fast charger (18 watt USB-C). The phone will stop charging at 80% to allow the battery to cool down. It will resume later, and charge at a slower rate to avoid overshooting 100%. The delay plus additional time might be another hour or two. This is normal.
2. You have Optimized Battery Charging enabled. This feature is intended for overnight charging, and will stop charging at 80%, then resume based on your usage pattern to reach 100% when you get up in the morning. However, if you have it on and you don’t charge overnight it can get “confused” and not finish charging.

The absolute best way to improve the life of your battery long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the night the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern.