Google shows this warning for any app installed from outside its store; it does not mean the app is harmful. Tap More details, then Install anyway.
If a Samsung device says “App not installed”, open Play Store → your picture → Play Protect → settings, turn scanning off, install the app, then turn scanning back on.
If you already have an older Android build, uninstall it before installing the new one. Your licence key stays valid — re-enter it from Settings → Subscription.