Wear OS App Sideloading Is Going Away Next Month
One of the benefits of the openness of the Android platform is that users technically aren't limited to getting apps just from Google Play Store or any app store for that matter. At their own risks, users could simply "sideload" or install APKs for apps that are distributed outside of those channels. That feature has more or less also been available on Android's wearable version but Google is soon making a major change that would make sideloading Wear OS apps next to impossible.
To be fair, Google wasn't exactly targeting app sideloading in its big change next month and it isn't exactly out of the blue either. Starting March 10, Google has announced that it will be retiring its "Legacy Embedded App Model" which was the only way smartwatch apps were distributed until recently. In a nutshell, this model lumped Wear OS apps together with regular Android apps, whether or not you have a smartwatch anyway.
This legacy model indirectly allowed installing Wear OS apps without going through any app store, which means bypassing Google Play Store's approval process. Developers can simply distribute an APK that smartwatch owners can install on their phones (again, at their own risks) and then go to Wear OS' settings to install the accompanying smartwatch app from the phone. With Google removing support for this app model, it will no longer be possible to do so.
There are valid reasons why Google is pushing the newer Wear OS app model. It allows Wear OS apps to be discoverable and distributable on their own while also reducing the size of the Android APKs themselves. Google has been trying to reduce and split up Android apps in order to make their distribution more efficient so it isn't surprising it wants to do the same for Wear OS.
That said, that also has the consequence of making Wear OS less open, whether it was intentional or not. Now the only way to install smartwatch apps is through Google Play Store, practically locking in developers and users to a single distribution platform for Wear OS apps.