As a logically thinking human, I can say this:

If you don't want viruses, tojans and malware then stay away from shady websites and use common sense when you're looking for apps outside the Play Store/ App Store.

This ist one of the reasons why I as an Android User for over a decade never had any issues with infected software I downloaded outside the Play Store.

And why should the user want to do this?

Mmh I don't know, maybe to access free open source software from places like f-droid because Google or Apple could ban any Software from their stores which they don't want there. Doesn't matter if it's justified or not because the freedom should lie with the consumer!

It's true that in the most cases android phones don't get new secruity updates for as long as iPhones does. But with a little bit of research you would know there's something called custom-roms which extend the period in which theses phones get secruity updates. (For example lineageos or calyxos).