As far as I know, GrapheneOS avoids letting users specify custom endpoints to mitigate the threat of phishing/social engineering. Private DNS is an exception because it's a default Android feature, but it poses the risk of users being tricked into setting a server controlled by a malicious actor who wants to surveil a user's network activity (in the form of DNS requests). Geolocation is similarly, if not more, sensitive information, so I don't think they will take that risk.