Why is South Korea clashing with Ukraine while North Korea learns modern warfare

This is not modern warfare. What happens in Ukraine is simply because neither side has a viable air force. If either of them had it, they'd win and drones won't do much of a difference. There's little relevant North Korea can learn about it.

This article does not mention that South Korea has been exporting to Russia manufacturing equipment used to help make the surface to surface missiles used to attack Ukraine.