i certainly never activated it willfully. i use Chrome only as a fallback testing platform for web dev - a handful of times per month - yet both Chrome Stable and Chrome Unstable had installed this 4GB monstrosity in my home dir. 8GB of junk i'd never used. Both have since been uninstalled and replaced with Chromium.
If you google OptGuideOnDeviceModel, there’s already a lot of results of people asking what it is an how they can delete them. It’s not some kind of obscure niche feature.
I wonder when the first crypto miner-like malware appears that offloads model usage to the client computers.