Enhanced Visual Value
If a product team has done a good job, users will clearly understand a new feature's value and they can turn it on whenever they choose.
By enabling Enhanced Visual Search automatically on every device running the most recent version of the MacOS and iOS operating systems, Apple appear to have determined that their product team were unable to describe the feature's value in a way that users would understand.
Perhaps the chosen value proposition for the feature was in the style of the recent Apple Intelligence ads, and that's why there was neither a public announcement nor a reference in release notes for those recent OS releases.
It's clear that describing a feature where Apple is analysing data in our Photos while retaining the privacy of those photos isn't going to be easy, but they still needed to tell users about it before turning it on. Even cryptographic experts who understand much of what Apple are actually doing with the feature appear to be mostly concerned with the secretive release.
Personally I have looked at the feature and have no issue with it, as it seems to simply be an extension of the existing Visual Look Up feature. But as I wrote when I first heard about it, while the feature itself may be completely benign, choosing to automatically enable without consent was a poor choice.
Back in the day, when new features were released in software you rarely had the choice of disabling individual features, so installing the software meant the feature was instantly available for you to use. Skipping the release was often your only option if you didn't want a feature to be active on your computer.
These days, with cloud services buttressing almost every piece of software we use, and your personal data (and photos) being exchanged continuously across the internet, it's doubly important that users should be told in advance about anything that might impact their private and personal stuff.
No matter how long the list of available settings, if you can't clearly explain how a new feature benefits users, the setting for that feature should be turned off by default.
This way your customer retains their existing functionality while having the freedom to enable this new feature whenever they've been convinced of its value.