I always saw black mirror as explicitly a near-future satire of the present, not commentary on where humanity is headed. I think something like Children of Men would fill the british angle better.
A handful of Black Mirror episodes land on a more optimistic (or at least not entirely bleak) note, though "happy" might be overstating it for any of them. Bittersweet, maybe.
Eulogy and Hotel Reverie from the newest season are at 70-75%, and I think they both end on a similarly bittersweet note like San Junipero. The one with Miley Cyrus is at 65% and is about as happy an ending as Black Mirror episodes get.
Black Mirror likes to show us the most-important thing as a kind of punctuation or statement of message even when it's not what the episode has encouraged us to believe is the most important thing (see also: the focus of the camera in the very first episode during A Certain Event—we've been primed for a grand, disgusting spectacle, and the camera chooses to show us none of that, and instead shows us something much more disgusting: the faces of people watching it, which is the actual show, and the point of the "artist" in the episode).
San Junipero ends by showing us the entirety of what is actually happening, for-real, which is an automated computer-maintenance system keeping itself running. It's highlighting the unreality of the virtual world, I think suggesting that even the apparent experiences we've been watching aren't happening in any real sense.
What's really happening? 100% of what's really happening? As you see. A computer system maintaining itself, to keep electricity flowing through its various circuits. Doing what? Doesn't matter, could be endlessly calculating digits of pi, that'd be just as much a "real" experience as what you've been so invested in. This is all that's really going on.
