

They can tie it to you by cross-referencing all the signals they have about you with data collected from other data collectors and aggregators. With enough data they can connect things like browser fingerprints and so-called anonymous ad IDs with your real identity.
Keep in mind that there is a good number of technical people whose job it is everyday to continuously figure out new ways to track everything they can about every person they can. These data collector and brokers have demonstrated time and again that they don’t really care about following the rules either. Here’s a good resource for more info https://noyb.eu/en
In terms of how they use it against you, this is some good info and it applies even if you aren’t American https://epic.org/issues/consumer-privacy/data-brokers/













If you want to be extreme, you only use devices that you control all the software on and you are very careful about what software you run. You always use a killswitch vpn. You choose carefully the websites you use and you use all the standard counter measures (ublockorigin,DoH,uMatrix,pihole,etc) at all times. You keep another laptop that has whatever you need to install to be able to use your bank and the online shopping you can’t live without. You use it for nothing else.
Even then its not perfect. I’m pretty sure that all Android, iOS, and Windows devices track the wifi access point name and mac address of all the ones you use. They also track the location of all the access points as seen by everyone elses location enabled devices. Easy for them to combine that to basically know where every visible wifi in the world is.