That is not correct. You can also use DUO free. That is what I am doing since some years. Here is the “How to use it”:
About protecting Bitwarden. I use 3 different 2FA methods for this purpose:
- DUO free
- Authy
- Yubikey
By doing this I get into Bitwarden even if 2 out of these 3 methods - for whatever reason - are not available. Furthermore: I create a weekly backup. So even if none of these methods work anymore I have access to my credentials with the exception of those that were changed after the lastest backup was created.