Applebot identifies with the user agent Applebot and respects robots.txt. Allowing it lets Apple's assistant and search features reference your pages.
Applebot-Extended is not a separate crawler. Like Google-Extended, it is a robots.txt token: disallowing it opts your content out of training Apple Intelligence and Apple's foundation models while still letting Applebot crawl for Siri and Spotlight. The two decisions are independent.