Cheese plate in Harvard Square?
Something I've discovered recently (why did it take me so long?) is that Rialto (considered one of Boston's top restaurants, and pricey) in the Charles Hotel has a great deal before 7 pm: small glass of wine and some complementary grazing of their antipasti (usually bruschetta). I'm putting you on to something good here.
Another good option is Finale (behind the Holyoke Center). It's a very good place for dessert, but they also have a dinner appetizer menu, which includes small bites including cheese.
I find Upstairs on the Square whimsical and trying to achieve character but ultimately failing. Henrietta's seems like a good choice, though I don't recall if they have a bar area (in any case, it's across the hall from Rialto). Sandrine's is nice and also has a decent-sized bar. Grafton Street is pub, so adjust your expectations accordingly.
This may be my NY bias, but I find most places in Boston ultimately disappointing. Either they are upscale and elegant, but then lack vibe or young and studenty but lack quality. All in all I believe the Finale manages to bridge the two reasonably well. You're clear stuck in Boston so good luck!
Upstairs on the Square has an artisinal cheese plate on their dessert menu, and is a portion of their tasting menus.
Harvest has one on their dessert menu:
Henrietta's Table also has one on their dessert menu:
Sandrine's also carries one:
Grafton Street has one on their dinner app menu: