SmartTube’s developer told me that the computer used to create the APKs for the project’s official GitHub page was compromised by malware. As a result, some official SmartTube releases were unintentionally released with malware.

The news post going around: https://www.aftvnews.com/smarttubes-official-apk-was-compromised-with-malware-what-you-should-do-if-you-use-it/

The new versions should be clean however:

Users who may have installed the malware-infected versions of the app are recommended to reset their devices and take additional steps to review their YouTube and Google account information. https://www.androidauthority.com/smarttube-malware-fix-3620773/

If you were logged into anything, probably best to change your password to be safe (and delete all sessions to unauth every device)!

Next time you see an alert like that, definitely research it before trying to work around it and install possibly infected software (i know there possibly wasn't any news when the alert went up, but i'd way a day then look it up again before continuing).