Good question. I find law in general quite ambiguous and full of edge cases and exceptions.

My basic understanding is that self-determination is the right of a nation to choose their own way of government.

[1] Self-determination includes the right of a people of an existing State to choose freely their own political system and to pursue their own economic, social, and cultural development. As such it does not, in light of the current state of international law, impose on all States the duty to introduce or maintain a democratic form of government, but essentially refers to the principle of sovereign equality of States and the prohibition of intervention which are already part of international law

[1] https://opil.ouplaw.com/display/10.1093/law:epil/97801992316...