Yes, I have seen one. Not around here and not in the last 12 years.
Coming home (late) from a band gig, I turned into my then girlfriends street in Boxford, MA no less and there was a mountain lion on the edge of the road.
In a flash, it jumped into the tangled roadside brush and was gone.
Of course the police dept denied hat I saw and left it unchecked.
Upon “googling” any sightings in the area, I found that some sightings were reported just south of there in local news articles.
I believe they are “out there” but not in any numbers. I have had game cams out for years and have not had any on cams...everything but!
Incidentally, the sighting was in mid-late May which is the fawning season for deer (of which there are many in that area).
Reports of sightings pop up now and again...there used to be an online “group” devoted to anything
”Eastern Mt Lion” but I don’t know if they still exist.
By the way, even though they don’t exist according to NH F&G they are a protected species, so don’t shoot unless your life is endangered.