On January 20, foreign media reported that Apple M1 Mac users found that they can sideload iPhone and iPad apps again. Apple lifted the server-side obstacle to preventing such activities, but the reason is unknown.
Last Friday, Apple enabled server-side protection measures to prevent users from side-loading iOS and iPadOS applications. Previously, users could put the applications they purchased on their mobile devices on Apple's Silicon Mac. Users can bypass developer restrictions and allow iPhone and iPad versions of apps to run on Mac devices.
Developers allow applications running on macOS and iOS/iPadOS operating systems to be completely immune to these changes. The changes on the server before and after are only applicable to the IPA files extracted from the iPhone or iPad owned by the user and then executed on the Mac.
Users quickly discovered that Apple's server-side changes on Tuesday were cancelled again, and users can side-load the iOS app again. But this may only be a temporary state, because Apple has a certain incentive to restore the restrictions and force users to download the version approved by the Mac App Store instead of the mobile version.