> MFA simply does not work - not in edge cases - in very basic straight forward cases

I completely agree. At my workplace, attempting to add your account to the MFA app fails. If you click on the big obvious 'add account' button, it asks you to sign in to the account you're setting up MFA for. And when you enter your username and password, it then redirects to the MFA setup page and asks you to set up MFA. And if you follow those prompts, you end up back at the sign-in page. And so on.

Instead, you have to skip past the obvious 'add account' button, and click on a + symbol in the top right, and from there you can add the account by scanning a QR code generated on the MFA settings page.