Install from Unknown Sources is Missing
If you've ever tried to install an app from somewhere other than the Google Play Store, you probably know about the setting called Unknown Sources. This turns off a security measure that keeps our phones safe, which allows app installs from websites or places like the Amazon AppStore.
It's a safety feature, but Google removed it. Instead, you'll have to add Chrome to a list of "trusted apps" that has the ability to install apps. We're not sure if this method is better or worse, but Google probably knows something we don't.
Here's how to sideload apps on Oreo without the unknown sources setting.