This modem does not allow the user to change th DNS settings, it is locked to Comcast. No other modem I have owned does this. Comcast promised a fix for this back in April 2018. Where is the fix Comcast???
FWIW, I personally have never heard anything about them ever wanting to change this policy. You can change the DNS servers in some of the individual network clients but not in the firmware that they push to gateway devices.