A dear friend asked you to evaluate an app he developed, but when trying to install it, a problem arose: Android's protection system, Google Play Protect, prevents you from proceeding, presumably due to a privacy issue.
There are several ways to install applications on Android: the simplest — and safest — method is to open the Google Play Store (or pre-installed alternative stores) and search for apps there. Finally, one can resort to manually installing APK files and their variants, which are the packages containing all the application's files.
You saw a friend's account hacked and realized that using passwords is no longer a safe choice, so you decided to find a more secure authentication method.
Did you just buy a new iPhone but all your contacts are still saved on your old Android smartphone? Don't worry, this situation happens to many when switching operating systems.