These charts are almost meaningless. They're double- and triple-counting binaries: the slope of the Objective-C line and the slope of the Swift line are identical because nearly every added binary uses both languages. That doesn't provide any meaningful information except that Apple is still using both.
It gets worse when they get to the percentages: they list 61% as Objective-C's number for iOS 17, but 61% of what? According to the raw data, Objective-C is used in 88% of all binaries on iOS 17, with Swift used in 25% (instead of the 17% they list). Their calculated numbers are derived from a denominator of 8723 binaries, even though they only have 6030 in their data set, because they wanted the numbers to add up to 100%. That makes a nice chart, but it has no meaningful interpretation.
You're essentially looking at a series of pie charts, and it does tell a useful story: that there is more code being written in Swift and SwiftUI year over year.
The problem is that the pie chart is lying—it makes it look like the percentage of binaries containing Objective-C is going down over time, but it's actually going up just as rapidly as Swift is, because almost all added files contain both Objective-C and Swift. The only languages that are going down as a percentage of binaries are C and C++, because fewer new modules are being added using those.
The reason why it looks like Objective-C is losing ground is that every Objective-C+Swift+SwiftUI binary increments the denominator by 3 instead of by 1, and there are more of those added every single year. Since each of those binaries only adds 1 to the numerator, Objective-C's share of the binary pie seems to be decreasing even though it's actually keeping up with Swift.
It's entirely possible and even likely that Swift is increasing faster than Objective-C in terms of lines of code, but this data can't be used to show that.
I would guess that Swift isn't increasing in lines of code as fast as ObjC, because Swift gets more done per line of code. But "per feature" I'd guess Swift is slowly inching out ObjC.
It gets worse when they get to the percentages: they list 61% as Objective-C's number for iOS 17, but 61% of what? According to the raw data, Objective-C is used in 88% of all binaries on iOS 17, with Swift used in 25% (instead of the 17% they list). Their calculated numbers are derived from a denominator of 8723 binaries, even though they only have 6030 in their data set, because they wanted the numbers to add up to 100%. That makes a nice chart, but it has no meaningful interpretation.