My battery looses its charge too fast

Firstly, what is the maximum capacity of your iPhone XR's battery in Settings > Battery > Battery Health? If it is below 80% or otherwise suggesting it needs servicing, it needs replacing.

If it's above 80%:

What apps are using the most battery? Check in Settings > Battery

To optimise battery life, Apple recommends reducing brightness as much as possible and using Wi-Fi: Maximising Battery Life and Lifespan

Turning off Background App Refresh for apps may also help, go to Settings > General > Background App Refresh.

Since the device is 5 years old I would go into settings>Battery>Battery Life. If the Battery Life is below 80% I would replace the battery.

How old is the device? If it is fairly new I would optimize your device. You could also check the battery health, you may need a new battery.

How fast is fast?