How can I transfer an app on my iPhone to my Macbook Air?

Are you asking whether you can back up iPhone apps to a Mac – not to run on the Mac, but to download to the iPhone later? It sounds like that functionality once existed, but was taken away.

Or are you asking whether you can run iPhone apps on a Mac? The Mac and iPhone are different platforms with different operating systems. So as a rule the answer would be "No." However, Apple Silicon Macs can run some iPhone and iPad apps. If you have an Apple Silicon Mac and the developer allows this, you would get those apps onto your Mac directly from the Mac App Store.

You can't. Apple removed that functionality in iTunes 12.7, and applications downloaded to an unit on iOS 9.0 or above are thinned for it.

(253266)

Realitytest wrote:

I don't have any details.

I think the question is self-explanatory.

Sorry but your question is no where near being self-explanatory.

Writing an effective Apple Support Commun… - Apple Community

The iPhone runs iOS. The Macs run MacOS.

What app are you asking about? Maybe there is a MacOS version of the app.

E.g., here is a screenshot of part of the front page for the Mac App Store – showing several iPad apps that will run on Apple Silicon Macs. Note the text saying "Designed for iPad."