(It was going to be a comment, but it turned out longer than I expected)
I think your question is wrong because the important thing is the content of the barcode itself rather than how this barcode is rendered on your device. In fact, the TSA (in the U.S.) or the person at the door never sees the app when I place my phone face down on the scanner – whatever it sees, what it sees ; is if the barcode contains data that corresponds to their internal systems and therefore allows you to pass through this particular checkpoint.
In my case, the barcode is rendered via the Apple Wallet app, so it is neither the original airline PDF file, nor the airline app .
I'm not sure if this is happening in the barcode era, but there was previously a website that allowed you to generate fake paper boarding passes that would allow you to exceed the points of TSA control. Of course, I don't expect them to take you on a plane, but I think the idea was to avoid being followed by TSA or something something like that.