“The Mishnah B’rurah does not say it for Bentsching (as far as I know). The citation that Gabei is misrepresenting is 91:12. “
I am familiar. I just wanted gabie to find out what (s)he’s misrepresenting.
“The M”B says a hat is needed in addition to a yarmulka.”
You forgot the opening word of that comment in the M”B, “bizmaneinu” – in our time. In his time, he points out, it was the way of respect to wear a hat. Even before JFK hat usage was in decline. JFK just put in the final nail in that coffin. Nowadays, no one (outside of a few of us holdouts) wears a hat. So I don’t think that anyone can claim that it is mandatory today. IMHO, a jacket (mentioned in the Sh”A) and tie would be more a derech of cavode today.