Ein Passwort reicht nicht mehr.

Use one of your 10 backup codes instead of the app code. If you have none left, ask an administrator to reset your 2FA from the module administration. You will set up a new one at your next login.

Any TOTP app works, for example Google Authenticator, Microsoft Authenticator, Authy, 1Password, Bitwarden, Aegis or FreeOTP. The QR code is generated on your server, without going through a third-party service. Each user can also pick a security key such as a YubiKey, or their device biometrics (Windows Hello, Touch ID, Face ID).

Yes, you just tick a box in the module administration. Users who do not have a second factor yet are asked to set one up at their next login. The dashboard shows how adoption is going, and you can reset an account's 2FA or make it enrol again.

Security keys and biometrics (WebAuthn / FIDO2) only work when Dolibarr is opened over HTTPS. This is a browser rule, the module cannot change it. As long as you are on HTTP, use the TOTP app or the backup codes.

Yes, install version 6.0.3 or later. Before it, Dolibarr 16 to 18 did not ask for the second factor, because the check relied on a hook that only exists from Dolibarr 19. After replacing the files, disable then re-enable the module.