Differential identification means you can be singled out based on profiles. Even if you don't have any accounts, big tech companies still have shadow profiles, and those shadow profiles can be linked to your offline identity, such that everything you've done that's been recorded, and everything you've done in (temporal, physical, or digital) proximity to other people who do have accounts results in a record of activities.

Sure, you can get a burner, but you have to make sure you never use it anywhere near anyone you know, that the sim is obtained anonymously, that you're never imaged by any of the ubiquitous cameras, etc. Merely having it powered on provides enough metadata to establish a shadow profile, and it's nearly impossible for a person to secure two separate identities. There's also the superman problem - the burner phone would only ever appear when anonymars is missing, and vice versa, creating a real and exploitable pattern if anyone like the FBI wanted to root around in your life. All they'd have to do is query which shadow profiles match the temporal gaps correlated with your disappearance from tracking.

There's really no escaping it. The only fix is legislation - outright banning mass surveillance, with lethal corporate penalties and long prison terms for C-Suite responsible for violations. Short of that, we live in a world that is implicitly compromised and insecure unless you have nation state level resources.