If United States invaded Greenland, would the other NATO countries be obliged to defend it?

Side note: If this administration does invade, just accept the invite to the group chat our drunken Secretary of Defense sends you.

Article 5 doesn't oblige members to take any particular action. It only says that an attack on one is an attack on all, and leaves it to each member to decide what actions, if any, they will take in response.

It says each member will assist the attacked party/parties, as it deems necessary.
My interpretation of the article is that assistance is mandatory. What type of assistance is up to the member to decide
https://www.nato.int/cps/fr/natohq/topics_110496.htm?selectedLocale=en
- Prayers and likes is assistance right?

Probably? I don't think anyone knows for sure. It's not like NATO countries have invaded each other before.

It's not an easy say since Greenland is not a nato member, however it's an autonomous state of Denmark, which is.

Anyone's guess, really.

Edit: just as an addition I want to clarify I am trying to help answer the question. I wish peace for the world and especially Greenland.

Greenland is part of NATO just the same way that all other Danish territories are.
- I am not sure about that.
  But might of course be wrong. As stated in another answer I am not an expert for this but tried to give an answer why this situation is not that easy.
  Edit: Jesus, being downvoted for not knowing and putting in effort. Somehow I know why the world is going the way it is. Bring it on!
But Denmark is deemed legally to protect its autonomy which is a nato country. It's a strange case...
I know it’s not the best source from what I read on the Wikipedia article Greenland being a Autonomous territory of Denmark is apart of Denmark and therefore a NATO member
Also found this article
On 20 March 2023 Greenland send their own diplomat within Denmark’s group. So not only are they a Denmark Autonomous territory but they also have their own diplomat in NATO.

Obligation or not, it would set a frightening precedent of they didn't.

Yeah, it's a no win. Either NATO becomes ineffective because it won't honour it's agreement or WW3 starts.

Article 5 is only an obligation to have a meeting if someone calls for a meeting. It is not as strong as propagandized.

Greece and Turkey often have clashes and it is never a NATO issue.

CIA pig vermin NATO chief, Rutte, said it would not be a NATO matter.

I've never seen my former prime-minister been referenced as that :') - most certainly not my political colour, but why CIA pig vermin? He is most certainly a competent manager of the status quo, but as a leader spineless and without a vision (for a better world)
- NATO leaders are only allowed to be CIA pig vermin meant to force submission of other members to US. CIA agents dominate all colonial political parties, but it is only the most loyal that rise to NATO chief.

Whether or not they have to defend, if they don't, Greece and Erdogan will go to war.

Check the article 5 requirement. I don't see any "unless another NATO country" exceptions.

Probably moot as all the US has to do is increase presence and wait for an "or else" moment, so that they can rely with "or else what?"

Kind of like Czechoslovakia in WW2.