> Physical Features: We collect information about your physical features and dimensions, such as your estimated hand size when you enable hand tracking.

> Environmental, Dimensions and Movement Data: We collect information about your environment, physical movements and dimensions when you use an XR device.

> We use information we collect when you use Oculus Products for the purposes described in the Facebook Data Policy under "How do we use this information?", including to provide, personalise and improve the Facebook Products (including seamless integration between the Facebook Products); to provide measurement, analytics and other business services (including ads)

https://www.oculus.com/legal/privacy-policy/

It's right there in black and white, they measure the dimensions of the participant and the environment, link it to a Facebook account, and use it to target ads.