Users can opt out of the Privacy Sandbox features if they know they are there and they understand the options, IMV the settings for this are unclear at best almost to the point of being misleading.
We all know the power of defaults which is why users have to opt-out of participating in Topics rather than opting in.
The browser is supposed to be the users agent but for most people the Topics API isn’t acting in their interests. I suspect if you asked people whether they we happy for any site that asked to know the sorts of things they browsed the web for they’d say no.
As for 3rd-party cookies they should have been killed off long ago, the reason the death is delayed is because Google is primary an AdTech company and other adtech companies persuaded the UK competition authorities that Chrome killing them off without a suitable replacement would be anti-competitive hence misnamed ‘Privacy Sandbox APIs’
Apple has its own set of issues e.g. why can’t content blockers block in app ads but Apple’s issues are a separate conversation