Typography – Visual Design – iOS – Human Interface …

In iOS 14 and later, the system fonts support dynamic optical sizes, merging a font’s discrete optical sizes — such as Text and Display for SF Pro and SF Compact, and Small, Medium, Large, and Extra Large for New York — into a single, continuous design. This design allows each glyph or letterform to be interpolated to produce a structure …

https://developer.apple.com/design/human-interface-guidelines/ios/visual-design/typography/