UPDATE: According to 9to5Mac, Apple is once again allowing this side-loading, although it's unlikely to last long. It's not clear why the change was made.

Apple has started blocking users from being able to sideload iOS and iPadOS apps onto their new Apple Silicon M1 Macs.

Side-loading means downloading and installing apps from an unofficial source or through circuitous means, rather than going directly through the regular channels.

Running Mobile Apps on Mac

In the case of side-loading on the M1 Mac, this could be done by using apps, such as iMazing, to install the necessary app files---called .IPA files---on your swanky new M1 MacBook Air, MacBook Pro, or Mac mini.

On the new Apple Silicon Macs, users are able to run apps normally found on iOS devices or iPads on their Macs. However, Apple gives developers the option to opt-out of this.

Related: Apple Unveils M1: The "World's Fastest CPU Core"

This is usually done for user experience reasons, since apps designed with mobile in mind don't necessarily work so well when translated to a desktop or laptop setting.

Many developers have therefore decided to opt-out of this arrangement, meaning that a large number of mobile apps aren't available to run on Macs---despite the fact that, technically, it is possible for them to do so.

Apple Pulls the Switch Server-Side

As confirmed by 9to5Mac, Apple has now made the server-side transition to stop this side-loading. That means that apps are no longer available unless via the Mac App Store.

Apps already installed in this manner will continue to work, while previously downloaded .IPA files can also be installed. But for anyone running macOS Big Sur 11.1 or the developer or public beta of macOS Big Sur 11.2, attempts to carry out this side-loading will result in an error message.

Oh, well, it was nice while it lasted.