It’s only worth it to app makers to have side loading if they can do it for large numbers of users, bypass the app store’s rules, and bypass apple’s take. I’m expecting apple to set it up in a way they can do none of those things, by making it cumbersome to sideload, not giving entitlements to apps not published through the store, and by taking a cut for sales from sideloaded apps.
But it does allow for niche applications such as NewPipe and F-Droid, for technical users who know the risks.
The malicious PDD app is really, actually, published to the alt stores by PDD Holdings itself. It loads the exploit config and post exploitation modules from PDD's own CDN.
It's not the same repackage-with-malware shit plaguing China/SEA market since forever. It's first party.
And the Google Play version contains the same exploit delivery codes, though no real evidence that it was activated.