I would assume IP address, browser fingerprint, and handle if you reuse it are all being tracked between sessions, even assuming no tracking cookies.
Obviously some of these are more trackable than others, but there’s the risk of re-establishing identity between sessions-- say if your user-agent resets when you close your browser, but you sign in to a site that keeps track of you and shares it.
I’m very lax about opsec places like here or Reddit, my username is enough for you to find my city without much effort, and almost certainly find me in person with significant effort, and is certainly an easy start for trying to find me elsewhere online. My main defense there is that my password is different across every site, but many people aren’t even that careful, and that’s like the barest level of careful
There are quite a few scripts to do so.
https://github.com/j0be/PowerDeleteSuite is one of the better ones, best run it quick though, it uses the API, and so might die at the end of the month
Uhh, ‘secretly’? Google tracks everybody, what’s the secret?