Thank you Kevin ...
I checked out the changes you pointed at ... and they already were in our installation.
I've also downloaded again the 2FA plugin, uninstalled and reinstalled it, but it still reports the same version (0.3) ... so I guess we've already had the last version.
Nonetheless, it seems the situation has not changed.
In the User Profile page I still can select and configure only the Email verification option.
Thanks for your help