In 2017, Apple 8, 8p and X with A11 processor were launched. In 2018, Apple XR, XS, and XSM with A12 processors were released. If you're referring to launch time, the XS is a year later than the 8p. 8P, as a non-full-screen classic model, is still praised in some places, and XS is the minimum requirement to support the new features represented by ios15 photo text conversion, if you want to experience the new features of ios15, you have to use XS.
8p, then x, then xs