As a single state no less.

My mistake. If that was your whole correction, why didn’t you just say that in the first place?

https://en.m.wikipedia.org/wiki/Foreign_relations_of_Greenland

As with anything regarding international law it’s kind of just agreements and power. You can just break treaties whenever and it will only matter if someone with power then tries to punish you for it.

But Greenland isn’t fully independent. The Netherlands Denmark controls its foreign policy and provides for its defense. They do have an option to vote to leave that relationship, but Denmark also sends a lot of money Greenland needs to make their budgets, so it’s not a trivial decision to just leave.

Edit: Wrong country

They didn’t. The Netherlands Denmark did, and the results of arbitration are both not prescribed (you can sue for a billion dollars for emotional damage in court, it doesn’t mean you’re going to get it) and can potentially be rejected by national courts.

Edit: Used the wrong county.