So like comparing an actor talking with a friend vs giving a speech, before WWII they would often use more transatlantic features (like /r/ deletion) in the formal speech style. After WWII, this patterns in the opposite direction! In other words American actors started to lean more into (2/x)

An American (r pronouncing) identity. As a side note, lots of tv folks still do “accent reduction” which really just means mitigating salient local features - stuff normal ppl pick up on - but linguists for the most part will still be able to pick up less marked local features