How do I update my iPhone XR?

iPhone XR tops out at iOS 18 (18.7.5, currently) and the current iOS 26 is not supported.

You will need a newer or new iPhone for iOS 26; that’s iPhone 11 or later, or iPhone SE 2nd or later.

iPhone models compatible with iOS 26 - Apple Support

Here is how to update to the current iOS 18: Update iOS on iPhone - Apple Support

iOS 18.7.5 is the latest version available for your device, so what version are you seeing when going to Settings > General > Software Update?