Just make a prompt, your OS is full of them already and you do it for other features. When installing the new version, show a notification or whatever with:
Apple Intelligence is here!
[Try It Now] [Maybe Later]
Yes, yes, I know many of us would rather have a [Fuck You, Get This Shit out of My Face and Never Ask Me Again] button, but I’m trying to be realistic here about something they could plausibly implement.