Your syc data is secure, yes, but not so your account data, because is also known by Google, amon yor IP other. Enough to track you through every page with Google APIs (most) also your email, whichi is an unique identificator in the web. Don’t trust any web or service which share data to third parties, less in US webs or services. This is one of the reason because I always prefer EU soft, webs and services. They are also not perfect respect privacy, but lightyears better as those from US companies, where something like privacy laws, GDPR and user protection don’t exist or only in very deficient manner.