Yeah, they're supposed to. One of the features is called "fingerprinting prevention" by Apple, which according to Apple's documentation hides some personalisations in the browser (like plugins, fonts, detailed OS info, etc) so that trackers can't use them to fingerprint.
Safari 17 on Sonoma, with advanced tracking protections activated (also outside of Private Windows). I've tried with and without adblockers.
CoverYourTracks tells me I have strong browser protections but a unique fingerprint. In AmIUnique, I've a unique fingerprint too. I can see that Apple's claims to fingerprint-resistance are absolutely bogus, as the websites were able to list my fonts, plugins, etc., all things that should be protected against.
I'm disappointed.
I've tried all my other browsers and, in all of them, my fingerprint remains unique with plenty of information leaking.