The guy complains about those login buttons but the app is very much possibly the worst design I may have ever seen when I looked on his site. It harkens back to bad knockoff Metro UI text designs where the designer failed to read any form of typographic guidelines.

The author seems a little in need of therapy and to walk away from this for a little while with just how angry, sarcastic, and tonedeaf it all reads and to be clear, I'm in therapy, it's great and helps.

Honestly, I don't know why he is offering social login on an app that advertises E2E chat anyways, you are just giving them all the Keys to the Kingdom.