hasunemiku2015
... its being implemented by GrapheneOS themselves. If you don't trust the team, I'm not sure why you're using GOS in the first place.
And even if we entertain the idea the GOS isn't trustworthy, then a content blocker would be the least of your worries when it comes to surveillance. Like perhaps, you know, the entire operating system you're using (or even simply the browser that the content blocker would be part of).