What, if anything, has changed regarding retrieving an older version of an iOS app from a local backup? In the past, I know that there was a procedure that allowed one to delete an iOS application from an iPhone and then restore on that iPhone the version of the application that is stored on a backup.  This is quite handy when you've upgraded to a new version of an iOS app only to find it behaves worse than the version you already were using before the upgrade.
I have made use of this, so I know that it was possible at least at one time.
Clarifications about how this is not certain other questions:
No, I am not asking whether one can get older versions of an app from the App Store.
No, I am not asking about restoring just the associated data for a single application.  (And if one can only get the stored version of the application without stored data, then I'd be welcome at least that much.)
No, I don't want to reset all the applications and data or go back to the entirety of a backup.
Yes I do want to get back the earlier/older version of a particular iOS app that has been on my phone.  I do remember that the process started with deleting the new version of the app off the iPhone.  The result is that the app is Not on My iPhone.  Then the process went on to restore that app from the local backup.
I'm running Big Sur 11.1 on a MacBook Pro with an iPhone 7 running iOS 14.2. The last backup is stored on the MacBook Pro (not on iCloud).
If this is no longer possible with Big Sur, then (as in the Title) my question becomes &quot;What changed and when did it change so that it became no longer possible?&quot;  Since I've done it before, I know that it used to be possible.
Thanks in advance!
iTunes 12.6.5.3 was the last version that had the ability to download apps.
On September 12, 2018 Apple released iTunes 12.7.0.166 which removed the built-in App Store browser and thus the supported ability to store downloaded copies of apps on the machine that iTunes is running on.
https://en.wikipedia.org/wiki/History_of_iTunes
See also the article (and comments for) Apple Releases iTunes 12.7 With Major Changes, Including No Built-In App Store
If you want to do this today, you need to archive the older version of said app BEFORE you want to restore it. You can do this with a tool like iMazing, that allows you to maintain a local library of apps that are installed on an iOS device.
Caveat: You must download the app to the local library while it is still available from the MAS. There is no way to retrieve it from the iOS device.