The X-Client-Data header is documented in https://www.google.com/chrome/privacy/whitepaper.html#variations https://www.google.com/chrome/privacy/whitepaper.html

The X-Client-Data header is documented in https://www.google.com/chrome/privacy/whitepaper.html#variations https://www.google.com/chrome/privacy/whitepaper.html#variat... and Chrome uses it to run experiments to make the browser better. It's not used for fingerprinting. (Still speaking only for myself)