[keynha]

Behavioral signals are the usual answer: risk-scored, invisible challenges; proof-of-work (cost without identity, though it taxes mobile); and signup-velocity/rate limits that stop cheap abuse before any challenge fires. The reason fingerprinting wins anyway is that it requires less operator effort, not that it is the only thing that works.

[arbol]

Behavioural requires interaction. Fingerprinting is instantaneous and cloudflare runs on page load for lots of sites