Nowhere. The release of iOS 17 will support iPhone XR/XS, which is one generation older than iPhone 11. GP probably means iPhone 11 will get iOS 18 next year and no more OS upgrades after that (based on the fact that iPhone X is not getting iOS 17, iPhone XS may not get iOS 18, and so on).

While Apple does not guarantee or publish a guarantee about how many years of major OS versions and security updates iPhones will get, it’s typically been about six or seven years of major OS version upgrades (from original device release) and another two or more years of security updates. The iPhone 11 was released in 2019 with iOS 13. When it’ll stop getting a new iOS version is up to Apple.