One thing to note about the data is that the way the author counts a "Swift" binary and an "Objective-C" binary is a bit misleading, as it dual-counts binaries that feature both, and most new binaries feature both languages. That's why the slopes of the two languages look essentially the same: because they're the same binaries.

By my rough count [0], the number of strictly Objective-C binaries increased by exactly 4 between iOS 16 and 17. The number of strictly Swift binaries increased by 9 [1], and the vast majority of binaries added use both languages. It's not clear from the data if there are substantial amounts of ObjC code in these binaries or if there are just one or two functions in each.

EDIT: The percentage tallies are calculated weirdly too—because they double- and triple-counted binaries that have multiple languages, they calculated all the percentages out of a total of 8723 binaries (for iOS 17) even though there are only 6030 in their data set. The correct percentages should be:

SwiftUI: 6%

Swift: 25%

C: 7%

C++: 17%

Objective-C: 89%

This is less satisfying because it doesn't add up to 100%, but the metric they used doesn't have any useful meaning.

[0] Using the following regex on the raw data files: / \|Objective-C\n/ [0] Using the following regex on the raw data files: / \|Swift(\|SwiftUI)?\n/ and