By the UN definition, Hamas is a genocidal organisation

The UN does not define "genocidal organisation", but instead defines genocide. Does an organization who intends to commit genocide meet the definition of a genocidal organization, or would it be an organization who has both the will and the means to, or would it be an organization who is committing genocide? That's not defined by the UN and the nuance of that is very important to the claim.

Its founding charter, published in 1988, explicitly commits it to obliterating Israel. Article 7 states that “The Day of Judgment will not come about until Moslems fight Jews and kill them”. Article 13 rejects any compromise, or peace, until Israel is destroyed.

Here's the charter. In the preamble it states "Israel will exist and will continue to exist until Islam will obliterate it, just as it obliterated others before it". The particular translation I'm using of this document has it written as "The Day of Judgement will not come about until Moslems fight the Jews (killing the Jews), when the Jew will hide behind stones and trees." I don't speak arabic and as such cannot comment if perhaps it's simply that the term they use for "fight" is also one that explicitly means to kill as well, or what, but the second part does make clear that the intent is to eventually oppress the Jewish people and send them into hiding.

I'd recommend reading through the entire document if you have time.