It does look like inbox.google.com is missing from our data set. We have an open issue to make sure that all of the Google products are added [1].
The messaging that is currently shown there is definitely wrong too because inbox.google.com does support 2FA. We have another issue for handling the "unknown" state when the domain simply is not in our data set [2].
What type of messaging and UI do you expect to see when the extension is unsure whether a given site supports 2FA or not?
Also, have you had the chance to see the UX for a site that does support 2FA? We currently have over 1,000 domains in our data set, so there is bound to be a service that you use. Feedback from the community will really help improve the extension! Thanks for sharing your thoughts.
No 2FA here :( But you can better protect your inbox.google.com account if you follow these steps:
Create a unique password Use a password manager