For a creator posting a video, Google gives specific guidelines on whether to tag it as AI:

"Was AI used to generate or edit your content in any of the following ways?

- Makes a real person appear to say or do something they didn’t say or do

- Alters footage of a real event or place

- Generates a realistic-looking scene that didn’t actually occur

To follow YouTube’s policy, you’re required to tell us about your use of AI. This includes realistic sounds or visuals made or edited with AI. [View examples](https://support.google.com/youtube/answer/14328491)"

So oddly an intro graphic only has to be tagged as AI if it shows a real/realistic person, place, or event, but (per the examples page) apparently any AI-generated music counts.