On iOS devices, you have to use a developer account to sideload the app and it only works for a short time, IIRC. I’m fuzzy on the details because the places where I’ve worked, it mostly just worked although the experience was way, way better on Android. At one point I was on a team that ran a system for deploying apps for sideloading, and for years I’ve been carrying both an Android and iOS phone, so I feel like I have a handle on these differences, but I also am missing out on some of the problems that our team already solved.
On macOS, you can download an app and run it. Depending on the provenance of the app and the security settings, you may get a message like “this app is from an unknown developer” with no apparent way forward. The solution is to right-click the app and select open from the context menu. When you open an app by right clicking on it, the OS gives you an option to open the app. This depends on security settings, but I think this is allowed by default.
There’s a lot of malware out there these days and I think it is good and correct that it should not be obvious how to run arbitrary software you downloaded. We know people will just click through dialog boxes to try and get where they’re going, which is way (for example) there’s no button to visit an HTTPS site with a broken certificate in most browsers these days. Some things should not come with instructions, because the risks are too great for unskilled users.
Some people apparently need help making judgment calls about what is and is not safe to install on their devices. I feel like Mac OS might strike the right balance here: you can install anything you want, but the OS throws up speedbumps if the app doesn't have the right signature, is not from the App Store, etc. These protections can be easily circumvented, but they send a signal that you should think twice about doing so if you don't really know what you're doing.
Not it would not still be as safe.
Malware and scams would come with instructions to install their custom bad app.
“Install this custom Deals app to save money”
I would love a single example of that happening(on android)
I just don't understand this argument. Never did and I don't think I ever will. If apple allowed you to install custom apps, it would change NOTHING for your 80+ year old mother. Literally nothing. Her device would still be just as safe and secure as ever before.