I did use Authy once for a service i used for a bit but it required me to put my phone online every time[0] i tried to authenticate because otherwise the authentication would fail, so the association Authy=TOTP made me think a reliance on a 3rd party service is required and the page mentioning only mobile phone apps also made me think there is also some sort of reliance on mobile phones.

[0] I have a very old Android phone that i always keep offline