Do 朋 and 友 differ in meaning?
As a noun, both 朋 and 友 mean friends. While 朋 is mostly a noun, 友 is often be used as an adjective for 'friendly, ' as in '友軍'(friendly force); '友方'(friendly side)
友 can also be a verb for 'befriend' in classical sentences.
To find the subtle difference between two characters with similar meaning in a compound word, like 朋友，you can observe the other compound words they associate with.
Examples:

朋比為奸  friends collude in criminal acts
朋黨 circle (of friends); alliance (of friends)

The phrases above show 朋 emphasis on the 'closeness' and  'alliance' between  friends

友善 (friendly), 友好 (friendly), 友愛 (friendship), 友誼 (friendship)

The phrases above, show 友 emphasis on the ' fondness' and 'emotional tie'  between friends'