As I understand it, the delivery mechanism won't matter: Play Store,ADB, F-Droid, Bluetooth, or website. If the APK isn't signed by a Google-approved developer, it's not going to install.
If there's some ADB command that one can issue to install unsigned APKs for now, it's a temporary reprieve at best. Two Android versions later, the update from Google will read "Only 0.02% of users installed apps using adb, but the corresponding malware incidence rate was 873% more than the Play Store. Due to the outsized risk, we're disabling adb installations going forward"
If there's some ADB command that one can issue to install unsigned APKs for now, it's a temporary reprieve at best. Two Android versions later, the update from Google will read "Only 0.02% of users installed apps using adb, but the corresponding malware incidence rate was 873% more than the Play Store. Due to the outsized risk, we're disabling adb installations going forward"