Mattermost suggests that the users use Google Authenticator which is no longer is available under a free license.
I would propose making a different recommendation.

• the MFA setting mentions "When true, users with AD/LDAP or email login can add multi-factor authentication to their account using Google Authenticator." But it should mention that any TOTP application will do.
• the MFA setup page only mentions Google Authenticator instead of giving a shortlist of possible apps, such as Aegis, a free and open source application.

As FOSS software, we should promote the use of FOSS software to users and not lead them to believe that only Google Authenticator can work.

See https://github.com/mattermost/mattermost/issues/16904