Are there any differences in meaning and use due to commas ?

1. The country Korea is well known for Kpop.

2. The country, Korea, is well known for Kpop.

3. My friend Daniel used to make fun of me.

4. My friend, Daniel, used to make fun of me.

I wonder which ones are grammatically correct and whether there're differences in meaning due to commas. I think they're all grammatical but there would be differences in use and meaning.

For example, I think 2 seems to be more appropriate to say when people talk about not only Korea, but also other countries. On the other hand, I would say 1 when I'm talking about only Korea because lisnters already know which country I'm referring to, as I'm talking about Korea only.

I'm not sure whether I think about this issue correctly, as the English grammar is very alien to Koreans.

Please help me out! and thank you very much for your help as always.