Xero's AI feature, JAX, is currently in beta mode and can't be disabled. So, for the time being, you'll have to put up with the banners and prompts even when you don't want them.
Confusingly, Xero's advice has been that you can opt out of the beta in the JAX settings; however, as far as I can tell, this only relates to when you have already opted in to using it and don't want to continue - not to opt out of its presence entirely.
You have opted in if you have opened the star icon in the menu bar and asked JAX a question. If this applies to you, you will see a 'Settings' link at the top of the JAX window next time you open it. Click the link and scroll down until you see a red 'Opt out of JAX' button.
This does not get rid of the menu icon or any of the banners and prompts, it simply turns off your ability to use JAX.
We'll update here if anything changes.