I did a fair amount of tinkering with the infinity portal 2fa a few weeks ago, and this looks a lot like it is not popping up the enrolment dialog box because the system sees the account as already enrolled.
i.e. That toggle just activates/deactivates the 2FA configuration that is already set up.
To reset 2FA, go to the Users management page, there's a 'Reset 2FA' button:
Once 2FA is reset, you can re-enable it and it will re-do the enrolment process, if I remember correctly.
For more information, see the section at the bottom titled "To reset 2FA for a user of the Infinity Portal account" at https://sc1.checkpoint.com/documents/Infinity_Portal/WebAdminGuides/EN/Infinity-Portal-Admin-Guide/C...
(Note that only a Primary Administrator account can reset 2FA).
Edit: This also handily indicates if 2FA is set up on an account - if the "Reset 2FA" button is greyed out when you select a user from the list, then 2FA hasn't been enrolled for that user.