I got an e-mail from RubyGems.org that you should enable multi-factor authentication (MFA). This MFA is only available using Authenticator app, not SMS-based authetication.

I never used Authenticator apps before. They recommend Google Authenticator [0] or Authy [1]. I check Google Authenticator on Play Store has no update since 2017. Authy is updated (last updated on April 2020). I found that Microsoft Authenticator [2] is also updated (last updated on April 2020).

The app should protect my data and privacy. I'm OK with open-source software.

So, my question, what is the app you recommend?

[0]: https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2

[1]: https://play.google.com/store/apps/details?id=com.authy.authy

[2]: https://play.google.com/store/apps/details?id=com.azure.authenticator