For completeness: The single policy setting name to disable model download is GenAILocalFoundationalModelSettings https://chromeenterprise.google/policies/gen-ai-local-founda...

The current state can be viewed at the internal debug URL chrome://on-device-internals/

Since January there's a user facing toggle in Settings > System > On-device AI in Chrome Canary https://www.bleepingcomputer.com/news/artificial-intelligenc..., described in Chrome Help Center at https://support.google.com/chrome/answer/16961953https://sup...