I don't think anywhere you've mentioned what I thought the real "rule" was, in international law:
By default, no one has the right to secede from their country. The only exception is when they've been persecuted by their country. In that exceptional case, they have the right to secede.
More broadly, I think that existing borders are sacred, unless something exceptional happens that necessitates changing them.
[EDIT] Just to add, this means that "national self-determination" is not a thing. In a democratic country like Ukraine, the right to secede has to be given by the central government. International law favours the status quo, and the status quo is that Ukraine is a country.
I don't think anywhere you've mentioned what I thought the real "rule" was, in international law:
By default, no one has the right to secede from their country. The only exception is when they've been persecuted by their country. In that exceptional case, they have the right to secede.
More broadly, I think that existing borders are sacred, unless something exceptional happens that necessitates changing them.
[EDIT] Just to add, this means that "national self-determination" is not a thing. In a democratic country like Ukraine, the right to secede has to be given by the central government. International law favours the status quo, and the status quo is that Ukraine is a country.