I understand your reasoning for doing this, but do not like the implementation. I also wonder if you have considered the side effects. After some time to reflect, I do not think this is a good idea in the present state.

First off, the warning banner is kind of insulting.

User278094 is a new contributor. Be nice, and check out our Code of Conduct.

With that you are automatically assuming that us "more experienced users" will not be nice to new users, and need a reminder to do so. In my opinion, that little bit and the link to the CoC is completely unnecessary. If we do not already know to be nice to everyone and follow the CoC a banner is not going to help.

Something like this would convey your intended message without coming across as condescending or belittling to us "more experienced users".

User278094 is a new contributor. Take a bit of extra time to show them the ropes.

You are creating a class of users. Yes we need to treat new users with a little more grace, help them along, and all the other little things that need to be learned to succeed on SE. But sticking a "New" label on them does not necessarily help anything.
I'm going to venture a guess and say that it will hurt their chances of getting their question answered. New users can't UV. New users are much more unlikely to accept your answer.
You take those two points and then stick a warning on every new post reminding people of that and it does not help the answer rate.

No matter how "nice" and "welcoming" everyone on SE is to new users. We still do have the same problem with new users. They do not know how our sites work, and in many cases they do not care. They just want their question answered.
This new banner may help some but it is coming at the problem from the wrong end.

Its like a "dangerous intersection" sign. It is reminding the drivers that something is ahead, but really the intersection should just be fixed.

Sure we can try everything to make all the existing and established SE users be extra especially nice to new users, but we still need to fix the low quality posts from the new users.

I understand your reasoning for doing this, but do not like the implementation. I also wonder if you have considered the side effects. After some time to reflect, I do not think this is a good idea in the present state.

First off, the warning banner is kind of insulting.

User278094 is a new contributor. Be nice, and check out our Code of Conduct.

With that, you are automatically assuming that us "more experienced users" will not be nice to new users, and need a reminder to do so. In my opinion, that little bit and the link to the CoC is completely unnecessary. If we do not already know to be nice to everyone and follow the CoC, a banner is not going to help.

Something like this would convey your intended message without coming across as condescending or belittling to us "more experienced users".

User278094 is a new contributor. Take a bit of extra time to show them the ropes.

You are creating a class of users. Yes, we need to treat new users with a little more grace, help them along, and all the other little things that need to be learned to succeed on SE. But sticking a "New" label on them does not necessarily help anything.
I'm going to venture a guess and say that it will hurt their chances of getting their question answered. New users can't UV. New users are much more unlikely to accept your answer.
You take those two points and then stick a warning on every new post reminding people of that and it does not help the answer rate.

No matter how "nice" and "welcoming" everyone on SE is to new users, we still do have the same problem with new users. They do not know how our sites work, and in many cases they do not care. They just want their question answered.
This new banner may help some but it is coming at the problem from the wrong end.

It's like a "dangerous intersection" sign. It is reminding the drivers that something is ahead, but really the intersection should just be fixed.

Sure, we can try everything to make all the existing and established SE users be extra specially nice to new users, but we still need to fix the low-quality posts from the new users.