“Note the depiction of the harp of David shows various strings. It is said, “Josephus describes the kinnor as having 10 strings, made from a sheep’s small intestine, and played with a plectrum (pick), though the Book of Samuel notes that David played the kinnor “with his hand”.”
Certainly, the phrase ‘with his hand’ is flexible enough to include using a pick. That’s in English, while Hebrew is even more flexible in meaning.
I like and trust Josephus, but he did live 1000 years after David and the playing of the kinnor may have changed or it may have been played with either a pick or with the fingers, as guitarists do today.
I know harpists do NOT use picks, nor classical guitarists, so that’s one more current day fact.
Saw Andrés Segovia in concert, and I can assure you he used no pick.