Thank you, I wasn't sure about it.
Warranty aside, what are the cons of a jailbreak on the XR? Is going to make it unstable?
Warranty isn't an issue. Hasn't been since early 2015. Yes, Apple's legal still says it voids warranty but the Apple genius won't care. The worst that would happen is that you are asked to restore your phone (assuming it's still functional). Apple will fix/replace jailbroken iPhones. In any case, a restore to stock will remove the jailbreak.
As for cons, as a jailbreaker since 2012, I don't see any. As long as you stay away from cracked/pirated apps, sketchy repos, sketchy websites and as long as you aren't prone to handing your phone to strangers and letting them out of your sight with it then you should be fine.
Lots of people here will tell you that it weakens your security. The nature of how a jailbreak works is by exploiting a bug. But jailbreaking does not compromise your phone by throwing the doors wide open which is essentially what those who disagree with jailbreaking would have you believe.
Updating might be a con. Generally you want to stay on the firmware you're currently on. It's necessary to restore to stock and then update if you want to update. But updating can mean losing your jailbreak if there is not one for the firmware you update to.
