There is an increasingly big difference between polls that ask about Starmer's job performance (e.g. approve/disapprove) and polls that ask about favourability.

On average in August, Starmer has a +21 net approval rating...

...but his net favourability rating is just +6

(1/3)

Starmer's approval & favourability averages in August (changes since July):

Approve 43% (-), Disapprove 22% (-1)
[Net rating: +21]

Favourable 34% (-2), Unfavourable 28% (-2)
[Net rating: +6]

Lots of people approve of Starmer's job performance but don't like him.

(2/3)

Interestingly, this is not the case for Boris Johnson. His approval and favourability numbers are virtually identical. August averages (changes since July):

Approve 43% (-), Disapprove 42% (-)
[Net rating: +1]

Favourable 40% (-2), Unfavourable 42% (-2)
[Net rating: -2]

(3/3)