This question was answered in your other Forum thread Sendin apk file as security file to friends - #4 by TIMAI2
Users get the message “this type of file can harm your device…” when they have GooglePlay protect enabled. The ONLY way to handle the message is to tell potential users to ignore the advice and install anyway. Sorry, you are battling Google security policy.
The advice available is:
Google’s security attempts to protect users. They use PlayProtect as part of that security.Applications Blocked by Play Protect
and How to resolve the warning "Play Protect" while installing an app?
PlayProtect goes into action when users attempt to load apps that do not originate at the GooglePlayStore. Not just your app, everyone's apps ... this is the message everyone receives who does not load an apk to their Android from the PlayStore.... Users can say OK and install or Cancel.
