Jagex claims to “share” your personal data to advertisers like Google without getting any “monetary” benefit. For Free! What great friendships these corporate entities must have.
You can opt out with this link here, just be careful not to accidentally delete your account (unless…?):
https://support.runescape.com/hc/en-gb/articles/360001370829
The Opt Out works for all UK and EU members, but if you live in the USA and Brazil there are some extra requirements such as living in Virginia or California for the USA. You can do this by entering your ZIP Code on the form. The California Zip Code, which you live in, Capische?
Under GDPR this kind of data collection and sharing HAS to be opt-in i.e. with an informed consent. You can’t just bury it in your TOS and/or privacy policy. The user has to be explicitly shown what they are collection, on what basis they are doing it and how they are using it, then give the user the choice to accept or decline that, and they have to respect that decision.
The users likely accept the terms during sign up and the form allows them to opt out later on.