- fingerprinting (especially if you don't own any premium inventory, as premium publishers generally dislike 3p targeting).

- contextual (target the content, make decisions based on _what I'm reading_ now, not who _I am_--less dubious ethically)

My favourite one: behavioural rebranded as contextual (I know some companies selling "contextual targeting", where some of the properties clearly define the user, these are mostly ML-based solutions, relying on mobile hardware)

Behavioural cross-platform targeting will exist but in a less deterministic form.

source: I used to work in AdTech and started a bunch of privacy-related initiatives.