If you look closely at the specs of the iPhone XR and the specs of the iPhone 11, you'll quickly realize that the iPhone 11 is an evolutionary update to last year's iPhone XR.
For starters, they have the same type of screen ("Liquid Retina HD"), and it's the same size (6.1 inches). The iPhone XR uses 2018's A12 chip, and the iPhone 11 uses 2019's A13 (Apple introduces a new version of its iPhone chip every year). While the iPhone XR has a single camera sensor, the iPhone 11 has two. And then there are the build materials: The iPhone 11 is made of glass and aluminum, just as the iPhone XR was.
In short: The iPhone 11 is a minor upgrade to the iPhone XR that adds a slightly more powerful chip, a second camera sensor, and a slightly longer battery life.
Given the $100 price difference between the XR and the 11, those upgrades may be enough to convince you to drop the extra cash.