The iPhone X, 8 and 8 Plus won't have iOS 17, as they have the old A11 Bionic chip, but that's no reason to worry. Yes, you'll miss out on the exclusives of iOS 17, but don't forget that they will cost the life and performance of your device in the future. If you have an iPhone 8 or an iPhone X or even an older one and you're excited about the new features in iOS 17, you might want to consider upgrading to a new iPhone this fall. Apple stopped offering feature updates for the iPhone 6 and iPhone 7 series with the release of iOS 16 last year.
Apple generally supports iPhones up to five years old with their latest operating systems, and of course, some features require even newer hardware to be compatible. Those iPhones will continue to be compatible with iOS 16, which Apple is likely to maintain for some time with security updates. If that's you, you won't be able to try out the new features in iOS 17 unless you buy a compatible iPhone. For example, while FaceTime on Apple TV works with any iPhone compatible with iOS 17, it requires a second-generation Apple TV 4K.
iPhone XS, iPhone XS Max and iPhone XR users can breathe a sigh of relief (for now), as these models were released a year later and will receive the iOS 17 update. To determine your iPhone model from physical details, see Apple's support article on how to identify your iPhone model. For example, improved automatic correction, which uses a new machine learning model and allows you to make online corrections and complete complete sentences, requires an iPhone 12 or later. When the iOS 17 update is released, it won't be possible to install it on iPhone 8 and iPhone X, or on any previous iPhone.
If your iPhone doesn't appear in the list above, it won't be compatible with iOS 17 and you won't receive a notification to download the latest software. Although older iPhones don't support the latest version of iOS or include any of the new features, they should continue to work for a while.