Point 4

> ... seek immediate UN Security Council action to provide assistance to Ukraine ... if they should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used

This seems like the passage which would cover it. The UN is able to authorize use of force by member states against the aggressor. Though it looks like it hasn't done that - probably because of Russia's permanent position on the UN Security Council which would veto any such measures.

Action was sought, as required.

Russia vetoed it, as expectged.

https://news.un.org/en/story/2022/09/1129102

I've read that point, and in my view it contains an obligation to call for a UN Security Council meeting and to seek a certain action by it.

The GP said:

>> The memorandum also said they would provide assistance

The memorandum does not contain an obligation to "provide assistance". "Providing assistance" and "seeking UNSC action" are very different things.

>> they are not keeping that promise.

They are not keeping promise to "provide assistance" because they have never made that promise.