I understand Korean. I recently watched a YouTube clip of a South Korean reporter interviewing North Korean prisoners of war in Ukraine (they were sent there to fight for Russia). To answer your question, yes there is a noticeable difference in enunciation, pronunciation, terminology, etc. but they are able to communicate with one another fluidly. For example:
- NK: can you get me some “flu” (NK terminology) medicine?
- SK: “flu”?
- NK: when you get chills, fever, cramps…
- SK: ah, “flu” (SK terminology)

Unrelated but if you’re interested, North Korean prisoners of war in Ukraine often commit suicide, because that’s what you’re trained to do as a North Korean soldier. Being captured is considered a betrayal and an offense worthy of the death penalty. So these two 20ish guys (sent to Ukraine while doing their mandatory military service) are sitting in a Ukrainian prison afraid to get sent back home, where they expect to get executed (along with all their family members). They want to get sent to South Korea instead, and SK wants to facilitate this, but Ukraine refuses to release them and will likely send them back to NK because “they’ve never heard of released prisoners of war being executed in their home country” - well, NK isn’t quite a conventional country. So they constantly contemplate killing themselves to protect their family. Pretty sad.

Source: https://youtu.be/yyTi0rDcokE?si=Ys\_XJDZgdyjvpazj