+1
It appears to be pin wear on the adjacent sprocket. Since it's below the chain engagement area it won't affect function.
But that kind of wear shows that the chain is in contact with the larger sprocket an awful lot. Possibly the chain is too wide for the cassette, or the trim needs to be adjusted outboard a hair. If the rim can't be adjusted without hurting shift function, and it's not noisy there's no harm in leaving bad enough alone.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.