Absolutely sure. It's this "Google Play Protect"-feature. I have multiple apps, and they used to trigger randomly these scan requests on upgrades for maybe two

Absolutely sure. It's this "Google Play Protect"-feature. I have multiple apps, and they used to trigger randomly these scan requests on upgrades for maybe two years, but with today's install it appears that they have changed how they deal with this, where you no longer have a choice. Maybe it's because it has extensive permissions wich I need in order to get access to my data usage, but that's not the point. Then again, it also happens with apps which don't require many permissions.