Yes, like this there is no app available. The developer of the app needs to release a new version for NC 19 (after testing the app). If there is no adjustment to the code needed, you can work around and increase the version number yourself.
However, the last version is compatible with NC15. Doesn’t look well maintained at the moment. With yubikeys you can also use other 2FA methods (U2F, Two-Factor TOTP provider).