MFA for External Portal Users

We have an external supplier portal in Appian where we need to implement MFA to hide sensitive sections on interface until verification is completed within the session.

Preference is to avoid app-based authenticators as some suppliers are hesitant to install anything.

Has anyone implemented something similar? Looking for suggestions on:

• Step-up MFA approach for external Appian portal users
• Conditionally showing/hiding sections based on completed verification
• App-free options like email OTP or SMS OTP that work well in Appian