Earlier quoted context omitted.
Looking at Android, where sideloading has been available forever, there doesn't seem any evidence of your worry.
Recent example: https://www.reuters.com/technology/google-suspends-chinas-pi... Malicious app in alternative store, the one in Google Play is different.
But it does allow for niche applications such as NewPipe and F-Droid, for technical users who know the risks.