Oh well all of this explains why I sometimes get instagram ADS which are relevant to me on my work phone even if I looked for stuff on my PC browser or smartphone (all using adblocks, deegogled android, private DNS, tracker blockers, private browsers and other preventive measures).

I didn't realize they could literally track you probabilistically or they could tie different devices to you..

So essentially if I use my amazon account on the same PC (or on a device tied to me) that I use for looking at "cat food" I am screwed and they will know I have a cat and amazon will start advertising cat stuff to me?

I did know they tracked you, but I thought it had to be a consistent set of datas: accounts, unprotected browsing, keeping cookies for a long time etc etc.. I didn't know they could probabilistically try to catch you nor that they could so reliably tie devices togheter.. I would like to know more about what they can actually do and what are preventive measures that actually works..

For example: can they (and how) get over tracker blockers? VPNs? Proxies? Private DNS? Degoogled devices/Linux?

What I've got to do if I want to be on the internet preserving my privacy? Should I literally stop using the internet? Should I use devices on which I do not login on a normal account ever and just use my self hosted stuff or the federated web?

And what about all the data they already have on me, it will be their's forever??

This is getting ridiculous, we need new solutions, the internet as we now know it is completely screwed.