fakruzaruret Thank you.
I took a look at this, and is appears to be working correctly, both with and without discussion cards enabled.
I see from your screenshot, that the example you are giving is of a discussion which is already unread, in which case, the 'mark unread' option will not appear anyway.
Examples:
Two discussions, as cards, on the left the discussion is read (color), on the right the discussion is unread (greyscale):
The read discussion on the left shows the 'mark unread' option:
The unread discussion on the right does not show the option, as it would not make sense to show the option on an already unread discussion:
I hope that clears things up for you on how the extension is supposed to function 🙂