AI update to Apple's Siri voice assistant unveiled on Monday garnered lacklustre reviews, spurring caution among investors who have seen tech valuations push equity markets into record territory.

At its annual developers' conference, Apple put the spotlight on new AI features, while highlighting security and child safety — and critiquing the company's AI competitors.

Polls have found the U.S. public uneasy about AI, and while Apple customers in other major markets such as China view AI more positively, Apple has historically never embraced…