As I have previously expressed, I think that people should be loud and proud about using tools that protect their security and privacy, be that someone's password manager, their VPN, their OS etc. That is the only way to normalize using these tools and defeat the narrative that only people who are doing something nefarious would be using tools like that.
Having said that, I also understand that some people might be in situations where being "loud" about something like this might have negative consequences for them, or increase suspicion. I am not advocating for putting yourself in danger by telling people what you use and why, if your threat model requires that you do not disclose it. The rest of us who can afford to should be loud about it to keep making using tools like this normal, so that eventually those who do have something to fear by saying they do, no longer do.
Now, it is important to note that hiding that you're using GrapheneOS isn't easy or really feasible for someone who's actively looking for proof that you do. People have periodically asked us to implement security theater features such as hiding the boot logo that appears when the device turns on or is rebooted, without realizing that there's a screen that shows GrapheneOS' boot hash that cannot be removed.