I'm posting this here since my 15.0 bug report to WRI evidently has not been addressed in the 15.0.1.0 release. The AI Assistant documentation refers to Front End appearances that simply do not exist in 15.X and evidently pertain to the pre-15 Notebook Assistant add-on.

See here: https://reference.wolfram.com/language/tutorial/AIAssistant.html

For example, the control-key sequences don't work, there is no Assistance tab in the menu bar, there is no Assistant suggestion (lightbulb icon) anywhere, et cet....

I'd really like to engage with the AI features but the most basic documentation hinders this, other than being resigned to flubbing about!